Pressure sensor arrangement using an optical fiber and methodologies for performing an analysis of a subterranean formation

ABSTRACT

A sensor arrangement using an optical fiber and methodologies for performing an analysis of a subterranean formation, such as a subterranean formation containing a hydrocarbon based fluid. The sensor arrangement may be used to measure one or more physical parameters, such as temperature and/or pressure, at a multiplicity of locations in the subterranean reservoir. The sensor arrangement may comprise a sensor array comprising an elongated outer casing for insertion in the subterranean formation and into a fluid in the subterranean formation. The sensor array may comprise an optical fiber defining an optical path that links one or more temperature sensors and one or more pressure sensors and transports measurement data generated by the temperature and pressure sensors. A data processing system may be connected to the sensor array to receive measurements from the sensor array and to compute one or more values of a property of an extraction installation operating on the subterranean formation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/129,481 which is a National Phase Entry of PCT/US2010/001200 filed onApr. 22, 2010. This application also claims the benefit of U.S.Provisional Patent Application Ser. No. 61/202,945 filed on Apr. 22,2009. The contents of the aforementioned applications are incorporatedby reference herein.

FIELD OF THE INVENTION

The invention relates to techniques and devices for deriving operationalparameters and/or geological parameters of a subterranean formation suchas an installation for extracting a hydrocarbon based fluid from asubterranean reservoir. More specifically, the techniques areimplemented by measuring temperature and/or pressure at a multiplicityof locations in a well located in the subterranean reservoir. The wellcan be an injection well, used to introduce in the reservoir a fluid tomobilize the hydrocarbon based fluid, a production well for extractingthe hydrocarbon based fluid to the surface or an observation well. In aspecific and non limiting example of application of the invention, thehydrocarbon based fluid is heavy oil extracted by a Steam AssistedGravity Drainage (SAGD) process. Other areas of application of theinvention include geological and mining survey, water tables mapping,water tables control, geothermal mapping, geothermic energy control, oiland gas characterization and extraction process control. Yet other areasof applications include industrial processes especially for monitoringand control in harsh conditions. The invention can also be used foracoustic information gathering such as an hydrophone, a geophone, or amicrophone for surveillance or acoustic survey of the materialproperties between the acoustic emitter and the sensor array, forexample, structural monitoring.

BACKGROUND OF THE INVENTION

Tar sands are geological formations located in subterranean veins cappedby impermeable rock, leading to a natural compatibility to form asubterranean pressurized steam chamber to heat up the tar sand veins andmobilize the heavy oil. In this specification “heavy oil” refers tobitumen that requires energy to separate from the geological phase andflow to the surface in contrast to light oil that is free to flow andnaturally pressurized and so only requires a direct path to the surfaceto be extracted.

The U.S. Pat. No. 4,334,485 issued to Roger M. Butler discusses a methodto continuously steam tar sand veins via a horizontal injector wellrunning parallel over a horizontal producer well near the bottom of thevein that pump up to the surface the heavy oil flowing into it bygravity. This is the process now known as SAGD in the industry. Butlerproposes an initial phase where steam is injected in both wells to heatup the zone in between and mobilize the heavy oil in it, called theconditioning phase which insures proper flow into the producer. Once,this “pool” of liquefied heavy oil covers the producer well, theinjection of steam into it is stopped and the heavy oil that flows intoit is pumped to the surface naturally or artificially by a using pump orgas lift. Steam is continuously injected by the injector well over theproducer well creating a steam chamber that grows up in the tar sandvein, mobilizing trapped heavy oil that then flows down to a producerpool by gravity.

The extraction of heavy oil from tar sands is challenging both from atechnological and a commercial perspective. Many operational parametersneed to be properly set to optimize the rate of oil recovery. Examplesof operating conditions include: the rate at which heavy oil isrecovered and the temperature and amount of steam injected in the steamchamber, among many others. However, the gathering of information aboutthe conditions in the subterranean reservoir is difficult. In practice,an SGAD installation provides the operator with a few data points only.While the data points are useful, in most cases they are not sufficientto make clear choices about the operational conditions to beimplemented.

Accordingly there is a need in the industry to provide novel techniquesand devices to provide a better understanding of the conditionsoccurring in a subterranean reservoir from which a hydrocarbon basedfluid is extracted.

SUMMARY OF THE INVENTION

In a first broad aspect, the invention provides a sensor array formeasuring one or more physical parameters in a subterranean formationcontaining a fluid. The sensor array has an elongated outer casing forinsertion in the subterranean formation and into the fluid. A firstsensor is placed inside the casing for performing a measurement of thefluid at a first location in the subterranean formation. A second sensoris located inside the casing, the second sensor being spaced apart fromthe first sensor to perform a measurement of the fluid at a secondlocation that is remote from the first location. An optical path, suchas an optical fiber links the first and the second sensors. The opticalpath transporting measurements generated by the first sensor and by thesecond sensor conveying.

In a second broad aspect, the invention provides a sensor array formeasuring one or more physical parameters in a subterranean formationcontaining a fluid. The sensor array includes an elongated outer casingfor insertion in the subterranean formation and into the fluid. Atemperature sensor is located inside the outer casing for performing ameasurement of the fluid at a first location in the subterraneanformation. A pressure sensor is placed an extremity of the elongatedouter casing, the pressure sensor including a deformable component whichundergoes deformation in response to a pressure variation establishedacross the deformable component. The pressure sensor also includes anoptical fiber connected to the deformable component such that adeformation of the deformable component is communicated to the opticalfiber to alter one or more optical characteristics thereof, the opticalfiber defining an optical path linking the temperature and the pressuresensors, the optical path transporting measurements generated by thetemperature and the pressure sensors.

In a third broad aspect the invention also provides a sensor array formeasuring pressure at a multiplicity of locations in a subterraneanformation containing a fluid. The sensor array including an elongatedouter casing for insertion in the subterranean formation and into thefluid. A plurality of pressure sensors are mounted at spaced apartlocations on the array to provide pressure measurements a differentlocations within the subterranean formation. Each pressure sensorincluding a sealed area within the elongated outer casing maintained ata reference pressure and a deformable component within the elongatedouter casing exposed to a pressure differential between the referencepressure and pressure of the fluid, the deformable component undergoingdeformation in response to variations of the pressure differential. Anoptical pathway is coupled to the deformable component, wherebydeformations of the deformable component alter one or more opticalcharacteristics of the optical pathway.

In a fourth broad aspect, the invention provides a device for measuringpressure in a subterranean formation containing a fluid, the deviceincluding an elongated outer casing for insertion in the subterraneanformation and into the fluid and a deformable component inside thecasing, the deformable component undergoing deformation in response to apressure differential established across the deformable component. Anoptical path is also provided in the casing. A mechanical link isprovided between the optical path and the deformable component, themechanical link altering one or more parameters of the optical path inresponse to deformation of the deformable component.

In a fifth broad aspect, the invention provides a system for computing aproperty of an extraction installation having a subterranean formationcontaining a fluid and a well. The system has a sensor array in thewell, the sensor array including a plurality of spaced apart temperatureand/or pressure sensors for measuring temperature and/or pressure at aplurality of locations in the subterranean formation. The system alsoincludes a data processing system connected to the sensor array toreceive measurements from the sensor array, the data processing systemincluding a CPU, a machine readable storage in data communication withthe CPU and a user interface, the machine readable storage being encodedwith a program instructions for execution by the CPU to compute one ormore values of a property of the extraction installation. Thecomputation uses as a factor the temperature and/or pressuremeasurements from the sensor array and a balance selected in the groupconsisting of mass, energy and momentum of the fluid in the subterraneanformation.

In a sixth broad aspect the invention includes a method for computing aproperty of an extraction installation having a subterranean formationcontaining a fluid and a well. The method includes placing a sensorarray in the well, the sensor array including a plurality of spacedapart temperature and/or pressure sensors for measuring temperatureand/or pressure at a plurality of locations in the subterraneanformation. The method also includes providing a data processing systemconnected to the sensor array to receive measurements from the sensorarray, the data processing system including a CPU, a machine readablestorage in data communication with the CPU and a user interface, themachine readable storage being encoded with a program instructions forexecution by the CPU to compute one or more values of a property of theextraction installation. The computation uses as a factor temperatureand/or pressure measurements from the sensor array and balance selectedin the group consisting of mass, energy and momentum of the fluid in thesubterranean format.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified perspective view of a subterranean SAGDinstallation;

FIG. 2 is a cross-sectional view of the SAGD illustration of FIG. 1;

FIG. 3 is a schematical view of the various wells present in a SAGDinstallation showing the location of various temperature and pressureprobes in the wells;

FIG. 4 is a block diagram of a data acquisition and processing systemfor use with the SAGD installation in FIG. 3;

FIG. 5 is a block diagram of a data processing module of the systemshown in FIG. 4;

FIG. 6 is a block diagram of a data processing module of the systemshown in FIG. 4, according to a variant;

FIG. 7 is a schematical view of a section of a production well in a SAGDinstallation, illustrating the ingress of heavy oil in the productionwell;

FIG. 8 is a schematical illustration of the SAGD installation showingthe relationship between the steam head, the heavy oil pool, theinjector well and the production well;

FIG. 9 is a flowchart illustrating steps of a process for monitoring theoperation of the SAGD installation for steam-breakthrough conditions;

FIG. 10 is a flowchart illustrating steps of a process for monitoringthe operation of the SAGD installation for steam-breakthroughconditions, according to a variant;

FIG. 11 is a flowchart illustrating steps of a process for monitoringthe operation of the SAGD installation for steam-breakthroughconditions, according to yet another variant;

FIG. 12a is a longitudinal cross-sectional view of a non-limitingexample of implementation of a sensor array;

FIG. 12b is a longitudinal cross-sectional view of another example ofimplementation of the sensor array;

FIG. 13a illustrates a motion modifier structure used in a pressuresensor of the sensor array illustrated in FIGS. 12a and 12 b;

FIGS. 13b, 13c and 13d are variants of the motion modifier structureshown in FIG. 13 a;

FIG. 14a is a schematical illustration of a flow meter in which thepressure sensor illustrated in FIGS. 12a and 12b can be used;

FIG. 14b is a variant of the of the flow meter shown in FIG. 14 a;

FIG. 15 is another variant of the motion modifier structure shown in theprevious figures;

FIG. 16 is a block diagram of a computerized system for performingmonitoring of an SAGD operation;

FIGS. 17a to 17d are illustrations of pressure sensors using differenttypes of pressure transducers;

FIG. 18a is a front elevational view of a sensor array including apressure sensor according to another example of implementation of theinvention;

FIG. 18b is a cross-sectional view taken along lines A-A in FIG. 18 a;

FIG. 19 is a perspective view of a movement magnitude modificationstructure used in the pressure sensor shown in FIGS. 18a and 18 b;

FIGS. 20 to 32 are perspective views of different components of thepressure sensor shown in FIGS. 18a and 18b , also illustrating thesequence of assembly of the various components into a complete pressuresensor;

FIG. 33 is a longitudinal cross-sectional view of a pressure sensoraccording to a variant;

FIG. 34 is a longitudinal cross-sectional view of a variant of thepressure sensor shown in FIG. 33;

FIG. 35 is an enlarged view of the some components of the pressuresensor shown in FIG. 34;

FIG. 36 is another enlarged view of components of the pressure sensorshown in FIGS. 34 and 35.

FIG. 37 is a flowchart illustrating the main processing steps performingan analysis of a subterranean formation;

FIG. 38 is a general diagram of a shale gas extraction operation inwhich is used a sensor array according to an example of implementationof the invention.

DETAILED DESCRIPTION OF AN EXAMPLE OF IMPLEMENTATION

Generally speaking, the invention can be used in geological and miningsurveys, water tables mapping, water tables control, geothermal mapping,geothermic energy control, oil and gas characterization and extractionprocess control.

A specific example of implementation of the invention will now bedescribed in connection with FIGS. 1 and 2 that illustrate a typicalSAGD heavy oil extraction process. However, it is to be expressly notedthat the invention is not limited to this type of heavy oil extractionand can be used in many other different extraction processes. Examplesof other processes include Cyclic Steam Stimulation (CSS), Toe to HeelAir Injection (THAI) and Vapor Extraction Process (VAPEX), among others.Also note that these processes are not mutually exclusive and can beused in combination with one another to extract heavy oil.

In addition, while the example will be made in connection with theextraction of heavy oil, the invention can also find applications in thecontext of light oil extraction and extraction of natural gas

FIG. 1 shows a typical SAGD installation 10. A tar sand vein 12 runsunderground. Typically, a tar sand vein is located at depths rangingfrom 200 feet to 1500 feet below the surface 14. An impermeable cap rock16 or other overburden exists immediately above the tar sand vein.

To extract heavy oil, the SAGD installation typically includes two mainwells, namely an injection well and a production well. The injectionwell 18 is vertically drilled through the cap rock 16 and once itreaches the tar sands vein 12, is oriented horizontally to run withinthe tar sand vein 12. The bend 22 between the horizontal section 19 andthe vertical section 21 is referred to as “heel” while the extremity 24of the horizontal section 19 is called the “toe”. The horizontal section19 can extend along considerable lengths to span as much of the tar sandvein 12 as possible. For example, the horizontal section 19 can beseveral hundredths of feet long and can even reach up to 3000 feet andeven more.

The diameter of the horizontal section 19 of the injection well 18 mayvary according to the application, but typically it is of 8 to 16inches. To prevent the horizontal section 19 from collapsing, it has anouter casing or liner (not shown). The outer casing is a tube made ofany suitable material, such as steel that is perforated with slots orother type of apertures. The slots are provided to allow an exchange offluid between the interior of the horizontal section 19 and thesurrounding tar sand vein 12.

The production well 20 is configured in a similar way to the injectionwell 18. More specifically, the production well has a vertical section26, a horizontal section 28, a heel transition 30 and a toe 32. Thehorizontal section 28 is drilled below the horizontal section 19 suchthat both horizontal sections 19, 28 run generally parallel to oneanother within the tar sand vein 12. In a specific example, thehorizontal sections 19, 28 are spaced by a distance of about 15 feet.Also, the horizontal section 28 is provided with an internal permeableliner that can be made in a similar way to the liner used for thehorizontal section 19.

Many variations of this basic SAGD configuration are possible. Forinstance, there may be multiple horizontal sections branching out fromeach vertical section of the injector and the producer wells 18, 20 ininstances were it is desired to expand the wells network to reach alarger portion of the tar sand vein 12. Also, the relationship betweenhorizontal sections 19, 28 can also be changed. More specifically, thehorizontal section 19 can be put at about the same level as thehorizontal section 28 or they can be inverted, for instance thehorizontal section 19 of the injection well can be put below thehorizontal section 28 of the production well.

FIG. 2 is a cross-sectional view of the SAGD installation shown inFIG. 1. This illustration better shows the relationship between thehorizontal sections 19 and 28 and also better illustrates the operationof the SAGD installation. To mobilize the heavy oil trapped in the tarsands, steam at a temperature in the range of 200 degrees Celsius to 350degrees Celsius is injected in the injection well. As the steam travelsdown the well, it enters the horizontal section 19 where it isdistributed to the surrounding tar sand vein through the apertures inthe liner. The injection is maintained for a sufficient period of timeto heat the tar sand medium and mobilize the heavy oil, and steaming ismaintained continuously during the extraction phase. The heavy oil, inliquid form will flow by gravity down and pool around the horizontalsection 28 of the production well 20 and enters the production wellthrough the apertured liner. Since the SAGD installation can beconsidered essentially as a closed chamber, i.e. the steam pumped in thesubterranean structure cannot readily escape owing to the cap rock, thesteam has the effect of pressurizing the reservoir and expelling theliquefied heavy oil to the surface via the production well 20.Mechanical pumps or gas lift can also be used to help out and increaseexpulsion rate.

As the heavy oil trapped in the tar sand vein 12 is mobilized andcollected at the surface 14, a void volume around the horizontalsections 19 and 28 is generated and progressively expands as the oil isextracted. The void volume is identified by 34 in FIG. 2. The voidvolume 34 is usually called “steam chamber”. By “void” is meant that asubstantial portion of the heavy oil has been removed but the otherconstituents of the tar sand vein remain in place. The resultingstructure is a porous network made up of sand particles with intersticesbetween them that allows steam to penetrate through it.

In FIG. 2 the arrows illustrate the growth of steam chamber as oil isextracted from the sand medium.

As steam injected in the steam chamber penetrates the porous geologicalnetwork, it eventually cools and coverts to a liquid phase. The liquidis attracted by capillary pressure and retained in the porous network.As such, at least some of the void volume generated as a result of themobilization and extraction of the heavy oil is filled partially withwater. The amount of water thus absorbed by the tar sand vein depends ona number of factors, one of them being the porosity of the tar sand vein12. The porosity can be characterized by a number of factors, consideredindividually or in combination. One of those factors is the void volumeper unit volume of tar sand vein material. This essentially is a measureof the capacity of the oil depleted tar sand vein material to take upwater. The void volume will normally be equivalent to the amount ofheavy oil removed, assuming of course that the tar sand vein was fullysaturated with heavy oil before the extraction was started. The otherporosity factor that can be considered is the pore size of the oildepleted tar sand material. A network of small pore sizes will have theability to retain better the water that has penetrated through it sinceit creates a more intense capillary force on the water by comparison toa network made of larger pores. On the other hand, a small pore sizenetwork will be less permeable (more time will be required for water toingress the network) than a larger pore size network.

Accordingly, the SAGD process can be viewed as an exchange between heavyoil and water. The water replaces in the tar sand vein 12 the heavy oilthat was removed therefrom. This process can be relatively efficient inpractice as it allows extracting up to 60% of the heavy oil content ofthe tar sand vein 12, but also as low as 10% of the heavy oil content ifthe process is badly adjusted to the geology of the reservoir.

FIG. 3 is a diagram illustrating the placement of sensors of ameasurement system according to a non-limiting example of the invention,in the wells of the SAGD installation shown in FIGS. 1 and 2. Theinjector well 18 is provided with a sensor array 36 that measurestemperature, pressure and advantageously both. The sensor array 36 isimplemented on an optical fiber that is run within the injector well 18.More specifically the optical fiber is placed in a protective outercasing and slid through the well cap in the well up to well toe 24. Theportion of the optical fiber that has sensing capability is the portionlocated in the horizontal section 19. The sensors in the optical fiberare implemented by Fiber Bragg Gratings (FBG). An FBG responds to aphysical force acting on the optical fiber and the magnitude of thatforce can be determined by examining the optical interrogation signalpropagating through the optical fiber. When the optical fiber issubjected to a temperature variation, it expands or contracts and thisproduces a strain on the FBG and its effective refractive index changesproportionally. The strain, and proportional effective refractive indexmodification, changes the response of the FBG to the interrogationsignal and thus allows determining the force exerted on the FBG andconsequently the temperature.

The pressure sensor works on a somewhat similar principle. Pressure issensed also by detecting strain or bend exerted on the optical fiberthat changes the response of the FBG. However, in the case of pressure,a mechanism is used to convert ambient pressure into strain acting onthe optical fiber or to bend the optical fiber. Various types ofmechanisms can be used without departing from the spirit of theinvention. One example is to provide a bellows which is a structure thatmoves with a variation of pressure. Typically, a bellows is a closedchamber in which or around which is created a predetermined (orreference) pressure. When the outside pressure varies, the chamberexpands or contracts. The optical fiber is mechanically connected to thebellows such that expansion or contraction of it will create strain onthe FBG in the optical fiber. A detailed example of a pressure sensorwill be discussed later.

The response of an FBG connected to a bellows is a compound response.One component is contribution of pressure and the other temperature.However since the temperature is known via the response of thetemperature reporting FBG, the pressure contribution can be isolated todetermine the ambient pressure.

In the example shown in the FIG. 3, a pressure sensor is collocated witha temperature sensor. This arrangement provides a sensing pair in closedproximity to one another such that the pressure and temperature for acertain location can be determined with relative precision.

The sensor array 36 is well suited for harsh environments where thetemperature and pressure can be high, such as geological and miningsurvey, water tables mapping, water tables control, geothermal mapping,geothermic energy control, oil and gas characterization and extractionprocess control. The sensor array 36 is compatible with almost all oiland gas well types such as SAGD processes using overheated steam up to350 degrees C. and its variant Cyclic Steam Stimulation process, VapourExtraction Process (Vapex) in which a solvent is added to the steam,hydraulic fracturing process for gas, oil or geothermal wells and waterand solvent flooding processes, among others.

The sensor array 36 includes a number of sensing pairs placed at knownpositions in the horizontal section 19. In a specific example ofimplementation, a sensing pair is formed on the optical fiber at acertain interval, such as 6 inches, 1 feet, 2 feet, 5 feet, 10 feet, 15feet, 20 feet, 30 feet, 50 feet, or more. This allows reading thepressure and the temperature at each interval in the horizontal section19. As it will be described below, the response of every sensing paircan be distinguished from other sensing pairs. It this fashion, eachsensing pair is unique and can provide a unique pressure and temperaturereading.

During the installation process the sensor array is inserted in the welluntil the sensor array reaches the toe 24. This can be done by feedingin the well a length of optical fiber that corresponds to the length ofthe injector well 18 that is generally known. At this point, one canassume that the sensing portion of the optical fiber lies fully withinthe horizontal section 19 and that the sensing pair at the extreme endof the optical fiber is close to the toe 24. Since the distance betweenthe sensing pairs is known, the position of each sensing pair, hencesensing location can be established relative to the toe 24 or any otherreference point on the injector well 19.

In FIG. 3 the sensing pairs in the horizontal section 19 are designatedby the reference numerals 38 a, 38 b, 38 c . . . 38 n. The sensing pairsand the optical fiber segments linking the sensing pairs are placed in aprotective outer casing, such as for example a tubing section made ofIncoloy or any other suitable material. It is advantageous to use asensor array 36 that has the smallest possible cross-sectional shapesuch as to interfere as little as possible with the flow of steam in thehorizontal section 19. The protective outer casing has a circularcross-sectional shape or may have another cross-sectional shape, such asan elliptic shape as it will be discussed later.

FIG. 12a illustrates in cross-section the sensor array 36. As indicatedearlier, the sensor array 36 includes an optical fiber 1200 placed in aprotective outer casing 1202. The protective outer casing 1202 is in theform of a tube, but other cross-sectional shapes are possible withoutdeparting from the spirit of the invention. The outer casing 1202, in aspecific example of implementation, has a diameter less than 1 inch,preferably less than 0.750 inches, more preferably less than 0.625inches, even more preferably less than 0.5 inches and for someapplications even less than 0.25 inches. A sensor array 36 having asmall diameter is desirable since this allows installing the sensorarray 36 in any one of the wells 18, 20. Specifically, for installationsin the production well 20, a small diameter sensor array 36 does notreduce significantly the flow of oil, hence it does not impede the rateof production.

The outer casing 1202 includes a plurality of rigid sections 1204 whichare separated by bellows 1206. In other words two adjacent sections 1204are connected to one another by a bellows 1206. The bellows are acomponent of a pressure sensor. Each bellows is associated with adistinct pressure sensor 1208.

More generally, each pressure sensor 1208 includes a deformablecomponent that deforms in response to a pressure differential. In theexample of implementation shown in FIG. 12a , the bellows 1206constitutes the deformable component. When the bellows 1202 is subjectedto a pressure differential acting across the bellows wall, it expands orcontracts depending on where the higher pressure area is located. Whenthe higher pressure area is located outside the outer casing 1202, thebellows 1202 would contract, in other words the adjacent sections 1204would move closer to one another generally along the longitudinal axisof the sensor array 36. Conversely when the higher pressure area isinside the bellows 1206, the bellows 1206 would expand thus moving thesections 1204 away from one another. The degree of movement of thebellows 1206 depends on a number of factors, namely the pressuredifferential and the physical construction of the bellows 1206. Thephysical construction is determined by the material used for making thebellows 1206, the wall thickness and the convolutions structure.Basically, the physical construction of the bellows 1206 determines theability of the bellows 1206 to yield when exposed to pressure. Factorstaken into account when designing the bellows 1206 would include thecompatibly of the bellows material with the environment, namely suitablechemical compatibility and corrosion resistance, among others. Otherfactors include the ability to withstand the pressure differentialwithout collapsing or bursting and the degree of deformation desiredacross the range of pressure differential to which the bellows 1206would be exposed in use.

The deformable component is not limited to a bellows structure. Possiblevariants include diaphragms or flexible membranes that manifest a degreeof deformation when subjected to a pressure differential or even apiston movable in a cavity as a result of a pressure differential. Inthis example, a piston is considered “deformable” in the sense that thearrangement of parts changes as a result of the pressure differentialaction, namely the position of the piston in the cavity changes.

When the deformable component is arranged as a diaphragm, the diaphragmcan be installed on any suitable location on the outer casing 1202 inorder to sense the pressure acting on the sensor array 36. FIG. 12ashows in dotted lines at 1210 a circle identifying the possible positionwhere a diaphragm can be placed. The circle shows the position of a portmade in the outer casing 1202 that is closed by the diaphragm. Thediaphragm, when exposed to pressure differential moves transversallywith relation to the longitudinal axis of the sensor array 36.

When implemented as a piston, the internal cavity of the outer casing1202 can be used as a receptacle in which the piston slides when exposedto pressure differential.

FIG. 17 provides several examples of deformable components. FIG. 17aillustrates a deformable component in the form of a diaphragm 1700separating two areas 1702 and 1704 across which different pressuresexist. Accordingly, the diaphragm 1700 is subjected to a pressuredifferential which causes the diaphragm to yield.

FIG. 17b illustrates a deformable component including a bellowsstructure 1706. The bellows structure 1706 can expand or contract inresponse to the pressure differential between the inside 1708 of thebellows structure 1706 and the outside 1710. Note that in thisarrangement the bellows structure 1706 is fully contained in an outsidecasing 1711.

FIG. 17c illustrates a deformable component that uses a piston 1712moveable in a cavity under the effect of a pressure differential createdacross the piston. As indicated earlier, the piston arrangement isconsidered to be a “deformable component” in the sense that thestructure changes (the piston undergoes displacement) as a result ofpressure differential changes.

FIG. 17d illustrates yet another possible arrangement where a outercasing structure 1714 is subjected to a pressure differential whichcauses the outer casing structure 1714 to resiliently compress along thedirection A. The outer casing structure 1714 approximates an oval figurewith larger opposing sides connected to one another by hinge areas 1716and 1718. The hinge areas flex when the large opposing sides movetoward/away form one another when the outer casing structure 1714 issubjected to a pressure differential.

Referring back to FIG. 12, In addition to the deformable component, thepressure sensor 1208 includes a mechanical link between the deformablecomponent and the optical fiber. The mechanical link induces changes inthe optical characteristics of the optical fiber, the degree of changebeing related to the motion imparted to the mechanical link by thedeformable component. The change in the optical characteristics is,therefore, related to the pressure differential acting across thedeformable component.

Optionally, the mechanical link can be designed such that itsCoefficient of Thermal Expansion (CTE) matches the CTE of the opticalfiber to which it connects. In this fashion, when the pressure sensor issubjected to temperature variations, both the optical fiber and themechanical link thermally expand by the same degree. A CTE match betweenthe optical fiber and the mechanical link can be achieved by using forthe manufacture of the mechanical link a material having the sameconstant of thermal expansion, by providing the mechanical link with ageometry such that its thermal expansion will be similar to the thermalexpansion of the optical fiber, or using both avenues, namelycontrolling the material and the geometry of the mechanical link toachieve the match. Note the CTE match does not need to be achieved alongall directions; the objective is to limit artificial strain on theoptical fiber (that may erroneously be interpreted as pressurevariation). Accordingly, the CTE match is relevant for thermal expansionof the mechanical link along directions or axes that can induce strain,such as for example axial strain in the optical fiber. In that sense,components of the mechanical link, which do not produce any strain whenthey thermally expand, do not need to be CTE matched with the opticalfiber.

The mechanical link can operate as a strain imparting structure thatinduces strain in the optical fiber. The strain imparting structurechanges the motion of the deformable component to produce a modifiedmotion. The modified motion drives the optical fiber to induce strain inthe optical fiber. For clarity, the term “strain” does not only refer toaxial strain but may be strain in any other direction of the opticalfiber, such as radial, bending, twisting or other.

The strain imparting structure can alter the motion produced by thedeformable component in different ways.

In a first example, the strain imparting structure changes the amplitudeof the movement. The movement amplitude change may be linear andcharacterized by a constant K. K can have a value more than one, inwhich case the movement produced by the deformable component isamplified. When the value of K is less than one, the magnitude of themovement generated by the deformable component is reduced. The changesto the amplitude of the movement can also be non-linear. In such case,the degree of amplification or reduction is not the same across themotion range; for example within a first segment of the motion range themovement amplification can be of a first value and in another segmentthe movement amplification is a second value.

In a second example, the strain imparting structure does not change theamplitude of the movement but limits it range. In this instance, thestrain imparting structure will stop any further motion when the travellimit has been reached. This is useful to protect the optical fiberagainst over travel which may break it or damage it otherwise.

In a third example, the strain imparting structure changes the movementfrom one type to another, for example a translational movement ischanged to a rotational movement or vice versa.

The reader skilled in the art will appreciate that the strain impartingstructure can be designed to integrate two or more these functions andperform them at the same time or in sequence. For instance, the strainimparting structure can change the amplitude of the movement, change themovement type and also limit the motion range.

The strain imparting structure can be a single or multiple componentdevice. For simplicity and reliability a single component is preferred,however multiple components can provide added functionality. An exampleof a single component is a resilient body that stretches or compressesin response to motion communicated to it by the deformable structure. Anexample of a multi-component device can be designed with multipledevices, such as levers, cams springs or others, linked to one another.A pivot is an example of a link between components.

Specific examples of the strain imparting structure are shown in FIGS.13a, 13b, 13c and 13d . In those examples, the strain impartingstructure is coupled to an optical fiber to apply strain to the opticalfiber.

In the example shown in FIG. 13a , the strain imparting structure 1300changes the amplitude of the motion imparted to it by the deformablecomponent. The strain imparting structure 1300 includes a unitarycomponent made of resilient material and shaped for form a bend 1302between two arms 1304 and 1306. The arm 1304 is fixed, in other words itis attached to a component or structure that does not move. The arm 1306is attached to the deformable component. When the deformable componentmoves as a result of pressure differential acting on it, it causes thearm 1306 to move along the arrow 1308. The direction of the movementalong the arrow 1308 depends on the direction of movement imparted bythe deformable structure. For the purpose of this example, assume that amovement tending to further spread apart the arms 1304 and 1306 isproduced when the pressure differential increases (the reverse movementis produced when the pressure differential decreases).

An optical fiber 1310 is connected at 1312 and 1314 to the arms 1304 and1306, respectively. A grating 1316 is formed in the optical fiber 1310.When the arms 1304 and 1306 move apart, the optical fiber 1310 isstretched between attachment points 1312 and 1314, thus creating strainon the grating 1316. The degree of strain acting on the grating 1316depends on the amount of stretching movement applied by the arms 1304and 1306; i.e. the degree to which they are being forced apart. Bylowering the position of the attachment points 1312 and 1314 (bringingthem further away to the bend 1318) the amount of stretch imparted tothe optical fiber 1300 is increased. The opposite effect is accomplishedwhen the attachment points 1312 and 1314 are brought closer to the bend1318.

The strain imparting structure allows decoupling the deformablecomponent from the optical fiber. In this fashion, the deformablecomponent does not need to be designed according to the amount ofstretch that should be applied to the optical fiber for the pressuresensor to function adequately. The deformable component can be designedaccording to other factors, such as the environmental conditions towhich it will be exposed in order to provide a satisfactory operation.The range of motion that is produced by that structure can then beadapted to the optical fiber via the strain imparting structure suchthat it matches the characteristics of the optical fiber (for example,limit the range of movement to a certain range to avoid overstressing orbreakage of the optical fiber).

FIG. 13b is another example of implementation of the strain impartingstructure. In this case the geometry and mounting arrangement of thestructure is such that the bend 1318 moves radially with respect to thelongitudinal axis of the optical fiber 1310. Accordingly, instead ofbeing stretched as in the case of the previous example, the opticalfiber 1310 is radially compressed at a degree depending on thedisplacement of the deformable component and the degree of movementamplification/reduction provided by the strain imparting structure. Whenthe optical fiber is designed such that it can carry an optical signalaccording to different polarization axes, the degree of radial strainapplied on the grating 1316 will induce a change in the spectral spreadbetween the reflective peaks associated with the polarization axes. Insuch case the spread between the peaks will be indicative of the radialstrain acting on the optical fiber.

Thus, in the example of FIG. 13b , the strain imparting structure altersthe type of movement created by the deformable component. The movementis a translational motion that is converted in a compression forceacting on the optical fiber. At the same time the amplitude of themovement is also changed. Specifically, the amplitude of the movement isreduced. The range of motion of the strain imparting structure acting onthe optical fiber to create the radially acting compression strain ismuch less than the range of the translational movement that thedeformable component undergoes.

FIG. 13c is another example of the strain imparting structure. Thisexample is structurally similar to the example illustrated in FIG. 13b ,with the exception of the optical fiber. The optical fiber 1320 includesa pair of gratings 1322 and 1324 that are tuned to reflect the sameoptical signal wavelength. The gratings 1322 and 1324 create an opticalcavity. A disturbance in those cavities, such as birefringence inducedby radial stress, can be monitored by interferometric phase changesbetween the reflection of each individual grating of the pair 1322 and1324.

FIG. 13d provides yet another example of implementation of the strainimparting structure. In such case, the optical fiber 1326 is placed overthe unitary component 1300 such that it overlaps with a portion of thearms 1304 and 1306 and passes over the bend 1318 which acts as a hingebetween the arms 1304 and 1306. Relative movement between the arms 1304and 1306 is transmitted to the optical fiber as bending strain, whichchanges the properties of the grating 1328. The optical fiber 1326 canbe mounted on the unitary component 1300 by adhesive, electroplating orby brazing (when the optical fiber is metalized. This provides a veryrobust mounting arrangement where the optical fiber is protected by theunitary component 1300. An example of suitable adhesive is polyamidebased adhesive that has been found to provide adequate bondingproperties of use in the sensor array for an oil/gas productionoperation.

FIG. 15 illustrates yet another possible example of a strain impartingstructure. In this case, the strain imparting structure 1400 does notuse a bend or hinge to impart a bending strain on the optical fiber.Rather it uses a pair of jaws 1402 and 1404 including respectiveprojections and recesses that dovetail in order to induce strain into anoptical fiber 1406. The optical fiber 1406 has two attachment points1408 and 1410 that define a segment 1412 between them. As the jaws 1402and 1404 move toward one another the optical fiber 1412 is stretched asthe projections enter the respective recesses.

In this form of implementation, the jaw 1404 is stationary, while thejaw 1402 is movable. The jaw 1402 is connected (not shown) to thedeformable structure such that motion of the deformable structureimparts movement to the jaw 1402. Resilient components 1414 and 1416,such as springs reverse the movement of the jaw 1402 when the deformablecomponent returns to its original position.

The profile of the projections and recesses determines the degree ofstrain imparting (amplification/reduction, linear or non-linear, end oftravel limit).

In a possible variant, the mechanical link can induce a bend in theoptical fiber. In this instance, it is the bend and not the strain thatalters the optical characteristics of the optical fiber. For example, atilted grating in the optical fiber reflects a portion of the opticalsignal in the cladding depending on the degree of bend; the higher thebend the larger the proportion of the optical signal that goes into thecladding. This variant can use anyone of the mechanical links shown inFIGS. 13d and 15 which cause the optical fiber to bend. While themechanical links in those examples also induce strain in the opticalfiber, the strain has little or no effect on the change of opticalcharacteristics of the optical fiber.

Referring back to FIG. 12a , the strain imparting structure isidentified by 1212. The structure 1212 includes a bend 1214 on eitherside of which are provided arms 1216 and 1218. The arm 1218 extendsthrough the bellows 1206 and connects rigidly to the extremity 1220 ofthe bellows 1206. The attachment point is shown at 1222.

The arm 1216 connects to a plug 1224 that is rigidly mounted in theouter casing 1202.

The optical fiber 1200 runs uninterrupted through in the internal spacedefined by the outer casing 1202. It will be appreciated that thediameter of the optical fiber is smaller than the internal diameter ofthe outer casing 1202. Also note that the optical fiber 1200 is looselylaid inside the outer casing 1202 to prevent the fiber to beoverstretched as a result of thermal expansion of the outer casing 1202.The optical fiber 1200 passes through a port 1226 made in the plug 1224.The port 1226 is then sealed. The sealing operation can be made by usingany suitable sealing material that will make the port fluid tight. Anexample is brazing; the optical fiber 1200 has a metalized portion thatregisters with the port 1226 when the optical fiber is fed through it.Molten solder is then applied which completely fills the void and thuscreates a gas tight seal. Another option is to use electroplating. Yetanother option is to use an epoxy or another synthetic material basedglue. Usually, epoxies or synthetic material based glue have thermallimits and may start deteriorating at higher operating temperatures,generally above 300 degrees C. For environments above that limit isgenerally better to use a brazing technique to provide a reliablefluid-tight seal.

The optical fiber 1200 is laid over the bend 1214 and bonded to it byusing adhesive, brazing or electroplating. The arrangement is such thatas the arms 1216 and 1218 move one with relation to another, bendingstrain is applied to the optical fiber 1200 which changes the propertiesof a grating 1228.

The optical fiber 1200 is also provided with another grating 1230,adjacent the grating 1228. The grating 1230 is used to provide atemperature measurement. In addition, the temperature measurementobtained in that location is used by the monitoring system to derive thedegree of strain resulting from the effect of pressure, since thetemperature also affects the grating 1228.

The optical fiber 1200 then exits the section 1204, passes through thebellows 1206 and enters the adjacent section 1204. The fiber then passesthrough another gas tight plug 1232 that is identical to plug 1224.

This arrangement therefore provides a gas tight chamber formed by theadjacent end portions of the sections 1204 and also including thebellows 1206. A reference pressure can be set inside this chamber orarea, during the manufacturing stage of the sensor array 36 by pumping agas or preferably creating a vacuum via a service port 1234. Once thedesired degree of pressure has been established in the chamber, the port1234 is closed, by soldering or using any other appropriate sealant.

The resulting chamber is therefore completely sealed. The pressuresensor responds to a pressure differential acting across the wall of theouter casing 1202. If the pressure outside is higher than the referencepressure in the chamber, the bellows 1206 will contract. The movement istransmitted to the optical fiber 1200 via the strain imparting componentto create a bending strain on the optical fiber 1200.

When a known inside pressure is established in the chamber, such asintense vacuum, the pressure sensor can, therefore measure directly theabsolute outside pressure. The absolute outside pressure combined withtemperature measurements has value in an SAGD process since it ispossible by using thermodynamics laws to compute the enthalpy or energyof the steam.

The pressure sensor 1208 can be replicated at as many positions asdesired along the sensor array 36. In the example shown the pressuresensor 1208 and the associated temperature sensor are co-located butthis is not absolutely necessary.

A variant of the pressure sensor 1208 is shown in FIG. 12b . Thepressure sensor in this example is generally the same as the onedescribed in connection with the earlier example, the difference beingthat the bellows 1236 is located at the extremity of the sensor array 36and therefore terminates the sensor array 36. In this case, the bellows,instead of being provided with a pass-through channel of the passage ofthe optical fiber 1200 is closed by a cap 1238. The optical fiber 1200also terminates with a grating 1240 which is used to measure temperatureat that location. The optical fiber does not penetrate the bellows 1236.

FIGS. 18a and 18b illustrate another example of implementation of asensor array that is provided with pressure sensing capability and withother sensing capabilities as well, such as temperature sensing. Thepressure sensor array 1800 can be used for similar applications such asthose in connection with the sensor array 36.

The sensor array 1800 is an elongated structure that can extend tosignificant lengths and it is particularly suited for geologicalapplications that require a long reach as well as a small profile.

The sensor array 1800 has an elongated metallic outer casing 1802 inwhich travels the optical fiber 1902 which carries thepressure/temperature measurements. In some cases, the outer casing 1802may have a diameter less than 1 inch, preferably less than 0.750 inches,more preferably less than 0.625 inches, even more preferably less than0.5 inches and for some applications even less than 0.25 inches. In thiscase, the metallic outer casing is round and has a diameter of about0.25 inches. Owing to the small outer diameter, the sensor array 1800can be inserted in wells or other areas to be monitored easily. Forexample, the sensor array 1800 can be inserted through swellable packersthat are used to create a seal between different sections of a well,while allowing the swellable packer to maintain its integrity. Thesensor array 1800 can be inserted directly into a pressurized wellwithout the need to de-pressurize the well. Owing to the small profileof the sensor array 1800, it can be passed through a double pressure capwhile gas/oil flows out of the well. Also, since the sensor array 1800has a relatively small transverse dimension, it occupies little space inthe well and as such does not impede in any significant manner theoil/gas flow in the well.

A pressure sensor 1804 is mounted to the metallic outer casing 1802. Thepressure sensor 1804 is a tubular structure that is fitted at the end ofthe outer metallic outer casing 1802. For stability and durabilitypurposes, the pressure sensor 1804 can be welded to the outer casing1802. In addition to creating a durable joint, the weld also produces ahighly resistant fluid-tight seal between the interior of the sensorarray 1800 and the outside environment.

The configuration of the sensor array 1800 as shown in FIG. 18b is anarrangement where the pressure sensor 1804 is placed at the extremity ofthe sensor array 1800. In other words, the pressure sensor 1804terminates the sensor array 1800. However, it should be clearlyunderstood that the construction described allows providing multiplepressure sensors 1804 along the sensor array 1800. Multiple pressuresensors 1804 can be connected in series to provide a measurement spanwhere pressure and temperature can be measured at different locations.The connections can be made directly to one another, in other words onepressure sensor 1804 connects directly to another pressure sensor 1804.Alternatively, the pressure sensors 1804 can be spaced apart from oneanother and interconnected via the metallic outer casing 1802. in thisform of construction, sections of the outer metallic outer casing 1802interconnect pressure sensors 1804.

The pressure sensor 1804 is an elongated generally tubular structurethat is hollow. The internal cavity houses the optical fiber 1902 thatcarries the pressure and/or temperature measurements.

One extremity of the pressure sensor 1804 is closed by an end cap 1806while the other end is closed by another end cap 1808. The end cap 1806is provided as a closure and as a support of the internal strainimparting structure, while the end cap 1808 acts also as a closure butadditionally it integrates a deformable component which converts thepressure differential between the outside and the inside intodisplacement. The deformable component includes a bellows structure thatcan contract or expand in response to pressure changes. The bellowsstructure movement occurs along the longitudinal axis of the pressuresensor 1804.

The bellows drives a strain imparting structure that extends from theend cap 1808 to the end cap 1806. The end cap 1806 provides an abutmentagainst which the strain imparting structure 1812 can be resilientlycompressed by the movement of the bellows structure 1810.

To facilitate the understanding of the structure and the operation ofthe pressure sensor 1804, reference will now be made to FIGS. 19 to 32that illustrate in greater detail the various components of the pressuresensor 1804 and the method for assembling the components together.

FIG. 19 is a perspective view of the strain imparting structure 1812.The strain imparting structure includes an elongated beam made ofmaterial that is resilient such that it can be repeatedly bent withoutcreating a permanent modification to its shape. Materials of choice formanufacturing the stain imparting structure include metals and somesynthetic materials. In selecting the proper material considerationshould be given to the thermal conditions in which the pressure sensor1804 will need to operate such as to avoid temperature relatedstructural failures. The geometry of the strain imparting structure 1812and the material from which the strain imparting structure 1812 is madewill determine the behavior of the strain imparting structure in termsof how the strain imparting structure alters the motion of the bellowsstructure 1810 and applies it to the optical fiber.

The strain imparting structure 1812 includes an elongated flat face 1900that constitutes a mounting surface for the optical fiber. In practice,the optical fiber, which in FIG. 19 is shown in dotted lines 1902 ismounted on the surface 1900 and extends along that surface over at leasta portion of its length. In the example shown, the length of the surface1900 over which the optical fiber 1902 is mounted is identified by thebracket A.

The optical fiber 1902 can be secured to the surface 1900 in a number ofdifferent ways without departing from the spirit of the invention.Examples include brazing (when the optical fiber surface is metalized),electroplating, adhesives or mechanical connection.

As shown in FIGS. 20 and 21, a cylindrical drive rod 2000 is providedand mounted by welding to the extremity of the strain impartingstructure 1812.

FIGS. 22 and 23 illustrate an abutment 2200 secured to the end of thestrain imparting structure that is opposite the cylindrical drive rod2000. The abutment 2200 forms the end-cap 1806 shown in FIG. 18 b.

FIG. 24 illustrates the bellows structure 1810. The bellows structureincludes a series of convolutions that can expand or contract axially(along the direction identified by the arrow 2401, in response to apressure differential. The bellows structure is made of metallicmaterial, such as stainless steel for its tensile strength and corrosionresistance. Accordingly, the bellows structure 1810 can be used in highpressure corrosive environments.

The convolutions 2400 are connected to tubular couplings 2402 and 2404.The tubular couplings 2402 and 2404 can be made from the same materialas the convolutions 2400 or different material. The arrangement is suchthat the tubular coupling 2402 is connected to the first pleat 2400,while the tubular coupling 2404 is connected to the second pleat 2400.In this fashion, as the convolutions 2400 expand or contract axially,along the direction 2401, that expansion/contraction moves the tubularcouplings 2402 and 2404 away/toward each other also along the directionof movement 2401.

As shown in FIGS. 25 and 26, the bellows structure 1810 is mounted to anouter casing 2500. The outer casing 2500, which is also illustrated inFIG. 18b , encloses the strain imparting structure 1812. The connectionbetween the bellows structure 1810 and the outer casing is made byinserting a narrowed end portion 2502 of the outer casing 2500 into thetubular coupling 2402.

FIG. 27 illustrates in greater detail the bellows structure 1810 and itsconnection to the outer casing 2500. Both components are secured to oneanother by welding. A circular weld joint 2700 which runs along the edgeof the tubular coupling 2402 permanently secures the components and alsocreates a fluid-tight seal.

A circular closure 2800 is mounted to open end of the bellows structure1810, as shown in FIG. 28. The circular closure 2800 includes a circularcavity 2802 which is dimensioned to receive the drive rod 2000. Thecircular cavity 2802 is formed in a central projection that isdimensioned to fit into the tubular coupling 2404. As illustrated inFIG. 29, the closure 2800 is welded to the tubular coupling 2404 whenthe central projection 2804 is received in it. FIG. 30 illustrates ingreater detail the circular closure 2800 when the circular closure 2800is mounted to the bellows 1810.

The strain imparting structure 1812 is then installed in the outercasing 2500 through its open end. This operation is shown in FIG. 31.The cylindrical drive rod 2000 is inserted first and it fits into thecircular cavity 2802. When the cylindrical drive rod 2000 is fullyseated into the circular cavity 2802 the abutment 2200 engages theextremity of the outer casing 2500, thus obturating it. The abutment2200 is then welded to the outer casing 2500, competing the assembly ofthe pressure sensor 1804.

The optical fiber 1902 is mounted to the strain imparting structure 1812before the strain imparting structure 1812 is inserted into the outercasing 2500. The optical fiber 1902 is threaded through a small aperture(not shown) in the abutment 2200 and thus extends outside the pressuresensor 1804, running through the metallic outer casing 1802 up to apoint outside the sensor array 1800 for connection to a measuringapparatus or system. The optical fiber 1902 is shown in FIGS. 18b and32. The aperture in the abutment 2200 is closed with glue or withbrazing (assuming the optical fiber 1902 is metalized at least over aportion that passes through the aperture) to crate a fluid-tight seal.

A reference pressure is established inside the pressure sensor 1804. Thereference pressure is an absolute pressure value which would allowdetermining the absolute pressure outside pressure sensor 1804. Recallthat the pressure sensor 1804 measures a pressure differential betweenthe inside the pressure sensor 1804 and the outside. By setting theinside pressure to a known and fixed value, it is possible to computethe absolute outside pressure on the basis of the measured pressuredifferential value.

The reference pressure can be set to a very low pressure (vacuum) bypumping air outside the casing 2500 during assembly or can be set to apressure above vacuum by pressurizing the outer casing 2500 with asuitable gas. Vacuum is usually the better choice since the referencepressure remains relatively stable during temperature fluctuations. Notethat if the reference pressure is not vacuum, it is still possible tocompute the absolute pressure but this requires a knowledge of theambient temperature (which is available from a local temperaturesensor).

In use, as the pressure outside the pressure sensor 1804 changes, thebellows structure 1810 reacts to this pressure change by moving axially.The bellows responds to a variation of a pressure differential actingacross the convolutions. The movement that occurs restores theequilibrium between all the forces acting on the bellows structure 1810,namely the fluid pressure tending to collapse the bellows structure 1810(this assumes that the outside pressure is higher than the insidepressure) and the mechanical resistance to deformation the bellowsstructure 1810 manifests. When the two forces balance each other, thebellows structure 1810 does not move any more and acquires a stablecondition.

As the bellows structure 1810 moves, the motion is imparted to theclosure 2800 that is mounted at the free end of the bellows structure1810. In turn, the closure moves the drive rod 2000 which causes thestrain imparting structure 1812 to bend. The degree of bend is thereforerelated to the degree of deformation imparted by the bellows structure1810 as a result of outside pressure forces.

The bend will induce a certain amount of strain into the optical fiber1902 that is measurable as discussed earlier in this specification. Toprotect the optical fiber 1902 against excessive strain, the range ofmotion of the strain imparting structure 1812 is limited by the outsidecasing 2500. As shown in FIG. 18b , the strain imparting structure 1812can bend only up to a point at which it contacts the outside casing2500. The position of the strain imparting structure 1812 is shown bythe dotted line 1820.

FIG. 33 illustrates a variant of the sensor array 1800 in which thedeformable component is housed inside the outer casing of the pressuresensor. This form of construction is more suitable for a pressure sensorthat is located away from the extremity of the array. Generallyspeaking, the pressure sensor 3300 has an outer casing 3302, that iscontinuous with the exception of a sensing port 3304 that leads to apressure measurement chamber 3306. The chamber 3306 is closed by adeformable component in the form of a bellows structure 3308. Thebellows structure 3308 is moveable axially (along the centerline of theouter casing 3302 in response to variation of pressure differentialbetween the pressure measurement chamber 3306 and the interior of thepressure sensor 3300.

In this example of implementation, the outer casing 3302 thus defines aninternal cavity that is divided in two chambers or areas, 3314 and 3316by a fluid-tight partition which is constituted by the deformablecomponent. In this example, the deformable component works in tension,in other words if the pressure outside the sensing array is higher, thenthe pressure differential will tend to expand the deformable component.A strain inducing structure 3312 is connected to the partition and themotion of the partition (deformable component) is converted into strainon an optical fiber 3310 via a strain inducing structure 3312. Anadvantage of this variant is that it offers a smooth outer surface withlittle or no external ridges or irregularities, with the exception ofthe port 3304. In addition, the motion of the deformable componentoccurs within the casing 3302. In this fashion, several pressure sensors3300 can be mounted serially in order to measure the pressure atdifferent points along the length of the sensing array where thepressure measurement at each measurement point is independent ofmeasurements at other points along the sensing array.

To elaborate, the design of the pressure sensor 1800 described earlieruses a deformable component that is located outside the casing 1804 andin response to a pressure differential that deformable component yields.If several such pressure sensors are assembled serially, the motion ofone deformable component will be communicated to the pressure sensorsdownstream. If the bellows structure 1810 expands (when the pressuresensor 1800 experiences a lower outside pressure) that expansion, albeitminute, will cause a corresponding displacement of the entire segment ofthe sensing array downstream. For certain applications, where thismovement can occur unimpeded, this has no consequence. However, in otherinstances where the motion is likely to be impeded, the accuracy of thepressure measurement may be affected. When the downstream segment of thesensing array is long and it contacts geological structures whichresults into friction, that movement will be impeded to at least someextent.

The design of the pressure sensor 3300 has the advantage of constrainingthe movement of the deformable component within the outer casing 3302,in other words the deformable components of the various pressure sensors3300 along the sensing array are allowed to move independently of oneanother. The motion of one deformable component does not create orinduce movement in another part of the sensing array. This allowsperforming accurate and independent pressure measurements at differentlocations of the sensing array.

The chamber or area 3314 that communicates with the port 3304 istherefore opened and in use would fill with the fluid (hydrocarbon basedfluid or steam) outside the pressure sensor. If the pressure in thatchamber 3314 is higher than the pressure in the reference pressurechamber 3316 (which is likely to be the case in most instances where thereference pressure is vacuum), the deformable component 3306 will expandup to a point where all the forces reach equilibrium. Should thepressure differential established across the deformable componentchanges, the deformable component will move accordingly.

The partition dividing the chambers 3314 and 3316 prevents the ingressof fluid in the chamber 3316. As such, the chamber 3316 constitutes aclean and protected environment in which the optical fiber 3310 islocated. This environment is shielded from the external harsh conditionsand as such the optical fiber is protected from possible damage.

FIGS. 34, 35 and 36 illustrate in greater detail a variant of thepressure sensor 3300. In FIG. 34, the pressure sensor 3300 is shownmounted between a pair of connecting segments 3400 and 3402. Aconnecting segment is in essence a section of the sensing array thatjoins a pair of pressure sensors 3300. In its simplest form, aconnecting segment has an outer casing that is continuous with the outercasing of pressure sensor 3300 and connects at one end with one pressuresensor 3300 and at the other end with another pressure sensor 3300. Forapplications where fewer pressure sensors 3300 are needed, severalconnecting segments 3400, 3402 can be connected to one another to form alonger span between adjacent pressure sensors 3300. A connecting segment3400, 3402 also provides an internal pathway to carry one or moreoptical fibers running the length of the sensing array as it will beexplained below.

Advantageously, the joints between a connecting segment 3400, 3402 and apressure sensor 3300 or another connecting segment 3400, 3402 are fluidtight such as to avoid the ingress of external fluid inside the outercasing.

The pressure sensor 3300 has an outer casing 3310 that is tubular or ofany other suitable shape. The outer casing defines an internal cavitywhich is divided in two areas or chambers 3312 and 3314. The chamber orarea 3314 is exposed to the pressure outside the pressure sensor 3300via a port 3304. In this fashion, the fluid outside the casing 3310 canpenetrate into the chamber 3314. The chamber 3314 has a circularsidewall 3320 that defines a circular recess 3322. A deformablecomponent 3318 is located into the chamber 3314. More specifically, thedeformable component 3318 includes a series of convolutions, as in theprevious examples, and it is fitted into the circular recess 3322. Theinside of the deformable component 3318 opens into the chamber 3312. Inthis fashion, the pressure in the chamber 3312 and the pressure in theinside of the deformable component 3318 is the same. However, thepressure in the chamber 3314 and the inside of the deformable component3318 are unlikely to be the same.

The deformable component 3318 is constructed in a somewhat similar waythan the deformable components described earlier, in that it has an endcap 3324 which is sealed and from which runs a drive rod 3326. The driverod 3326 connects to a strain imparting member 3328 to which is mountedan optical fiber 3330 (shown in dotted lines).

The operation of the pressure sensor and the strain inducing structure3328 are similar to the operations of corresponding components describedin detail in connection with the previous embodiment and for that reasonthe description will not be repeated. One difference is the reversal ofthe movement imparted to the deformable component 3318 as a result ofthe pressure differential. If the pressure in the chamber 3314 is higherthan the pressure in the chamber 3312 (reference pressure chamber) thedeformable component 3318 will collapse (works in compression) insteadof tending to expand. Also, as in the previous case, the chamber that isat the reference pressure and which is isolated from the chamber 3314houses the optical fiber 3330.

Each end of the pressure sensor 3300 is provided with a sealedpassageway to allow the optical fiber 3330 to pass from one pressuresensor to another or from one pressure sensor to a connecting segment.Specifically, as shown in FIG. 36, one extremity of the pressure sensor3300 has a small aperture 3600 in which the optical fiber 3310 isthreaded and thus enters the chamber 3312. This aperture can be sealedwith adhesives, electroplating orby brazing. Similarly, the other end ofthe pressure sensor 3300, as shown in FIG. 35 has an aperture 3500 toallow the optical fiber 3330 to leave. Similarly, the aperture 3500 canbe sealed once the optical fiber 3330 has been inserted there through tocreate a fluid tight seal. In this fashion, the optical fiber 3310enters from one end of the pressure sensor 3300 and leaves from theother.

During manufacture a segment of optical fiber is attached to the strainimparting structure 3328 by using adhesives, mechanical fasteners,electroplating, brazing or any other suitable technique. The opticalfiber segment 3330 is threaded through the apertures 3600 an 3500, whichsubsequently are closed by adhesive or any other suitable medium. Theoptical fiber leads are then spliced with the upstream and thedownstream optical fiber segments such as to create a continuous opticalpath along the entire length of the sensing array. In this fashion, thesame optical path is shared with all the pressure sensors 3300. Todisambiguate measurements and be able to identify the location of eachmeasured pressure value, suitable multiplexing techniques can be used.In this fashion, a pressure measurement can be associated with aparticular pressure sensor 3300. Since the location of the pressuresensor 3300 in the sensing array is known, it becomes possible to mapthe pressure measurement with the geographical location where thatmeasurement has been taken.

It is also possible to use more than one optical fiber in the sensingarray, where one fiber measures temperature and the other pressure.

Note that since each pressure sensor 3300 has its own reference pressurechamber 3312 which is individually sealed, those pressure chambers donot need to all be at the same reference pressure. Applications mayexist where the chambers of individual pressure sensors may be set atdifferent reference pressures.

The sensor array 1800, especially when it uses the pressure sensor 3300is modular in that it is made up of several modules, connected to oneanother in series to form the elongated sensing structure. Each modulemay be provided with pressure and temperature sensing capabilities. Thetemperature sensor can use a Bragg grating located on the optical fiber3330 run in the chamber 3312. The use of modules allows building longsensor arrays from standardized components.

In use the sensor array 36, 1800 is inserted into the production well 20and it is held there during the operation of the well. In other words,the installation of the sensor array 36, 1800 is permanent and it isused to generate pressure and temperature data during the operation ofthe well and while heavy oil flows out of the production well 20. In apossible variant, the sensor array 36, 1800 can be temporarily insertedin the subterranean formation to take measurements and then removed tobe re-inserted again later or to be used in a different subterraneanformation.

As discussed above, owing to the small outer diameter of its outercasing, the sensor array 36, 1800 can be inserted easily in the well anddoes not impede in any significant manner the flow in the well.

Also, the small outer diameter of the outer casing of the sensor array36, 1800 facilitates transportation of the sensor array to the well'ssite. For example, in some embodiments, the sensor array 36, 1800 may bewound on a reel (e.g., a spool) transported to the well's site by atruck or other vehicle. Due to the small outer diameter of the outercasing of the sensor array 36, 1800, a continuous length L_(s) of thesensor array 36, 1800 wound on the reel may be relatively long. Forinstance, in some examples, the continuous length L_(s) of the sensorarray 36, 1800 wound on the reel may be at least 100 meters, in somecases at least 500 meters, in some cases at least 1 kilometer, in somecases at least 2 kilometers, in some cases at least 3 kilometers, insome cases at least 4 kilometers, in some cases at least 5 kilometers,and possibly even more (e.g., tens of kilometers). The reel has an outerdiameter D_(r) measured with no length of sensor array wound thereon.For instance, in some examples, the outer diameter D_(r) of the reel maybe less 1.2 meters, in some cases less than 1.1 meters, in some casesless than 1.0 meter, in some cases less than 0.9 meters, and in somecases less than 0.8 meters. A long continuous length L_(s) of the sensorarray 36, 1800 may thus be wound on a small diameter reel. For instance,in some examples, a ratio L_(s)/D_(r) may be at least 2 kilometers oflength of the sensor array per meter of outer diameter of the reel, insome cases at least 3 kilometers of length of the sensor array per meterof outer diameter of the reel, in some cases at least 4 kilometers oflength of the sensor array per meter of outer diameter of the reel, insome cases at least 5 kilometers of length of the sensor array per meterof outer diameter of the reel, in some cases at least 6 kilometers oflength of the sensor array per meter of outer diameter of the reel, andin some cases at least 7.0 kilometers of length of the sensor array permeter of outer diameter of the reel, and possibly even more (e.g., 10 ormore kilometers of length of the sensor array per meter of outerdiameter of the reel). The outer diameter of the outer casing of thesensor array 36, 1800 can allow the sensor array 36, 1800 to be wound onthe reel such that the sensor array 36, 1800 has a small radius ofcurvature. For instance, in some examples, the sensor array 36, 1800 maybe bendable to acquire a radius of curvature of less than 20 inches, insome cases less than 15 inches, in some cases less than 10 inches, andpossibly even less, without damaging the sensor array 36, 1800.

The sensing array 36, 1800 produces co-located pressure and temperatureprofile information. In a possible variant, flow rate information can beobtained by measuring a pressure differential between two spaced apartlocations in the body of heavy oil flow through the production well 20.This arrangement is shown in FIG. 14a . The production well 20 isprovided with a narrowed section 1400. A sensor array 36, 1800 passesthrough the production well. Assume that the array 36, 1800 has a firstpressure sensor 1402 on one side of the narrowed section 1400 andanother pressure sensor 1404 on the other side of the narrowed section1400. The arrangement is such that the pressure in the production wellcan be determined on each side of the narrowed section which provides apressure differential value that can be directly related to the flowrate.

FIG. 14b provides another example of production well arrangement with aninternal constriction 1406 that can be used to measure flow rate.

While an internal constriction such as the one shown in FIG. 14b or thenarrowing shown in FIG. 14a may not be ideal since they would reduce theflow of heavy oil in the production well 20, the concept can be appliedto any area of the production well where a pressure drop is known tooccur. For example a bend in the production well is likely to generate apressure drop and that pressure drop, albeit minimal can be measuredwith the pressure sensor according to the invention in order todetermine flow rate.

Note that the pressure sensor described earlier in connection with SAGDand other oil/gas operations can also be used in other applicationsunrelated to the oil/gas industry.

Referring back to FIG. 3 a sensor array 40, similar to the sensor array36, 1800 is laid in the horizontal section 28 of the production well. Inthe example shown, the sensor array 40 includes co-located pressure andtemperature sensors, forming sensing pairs 42 a, 42 b . . . 42 n. Thesensing pairs 42 a . . . n are placed at known intervals from oneanother. In a specific embodiment the spacing is constant and it is thesame as in the case of the sensing pairs 38 a . . . n. Also, the sensingpairs 42 a . . . n are located at known positions with relations to areference point of the production well 20. In this fashion, when asensing pair 42 a . . . n, reports a particular data and pressure valuesit is possible to determine the location in the horizontal section 28where the reported temperature and pressure conditions exist.

A predetermined relationship also exists between the sensing pairs 38 a. . . n and 42 a . . . n. As shown in FIG. 3, the sensing pairs 38 a . .. n and 42 a . . . n are located such that they alternate vertically, inother words a sensing pair 42 a . . . n is located at midpoint between apair of adjacent sensing pairs 38 a . . . n. This arrangement may vary,for instance the sensing pair 38 a . . . n, may be located in verticalalignment with the sensing pair 42 a . . . n, instead of being shiftedrelatively to one another.

Other variants are possible, namely:

-   -   1. The temperature and the pressure sensors may not be        co-located. For example the sensor arrays 36, 40 and 1800 may be        constructed such that the temperature and the pressure sensors        alternate with one another, such as for example each temperature        sensor is followed by a pressure sensor, a pair of consecutive        temperature sensors are followed by a pressure sensor, etc.    -   2. The number and the spacing between the sensing pairs 38 a . .        . n, 42 a . . . n may vary. In the example shown, the spacing        between the sensing pairs 38 a . . . n, 42 a . . . n is constant        but this may be changed to provide more or less measurement        resolution in certain areas. For example, if it is desired to        read the temperature and pressure with a higher resolution near        the heel of the injector well 18, the density of the sensing        pairs 38 a . . . n can be increased in that area.    -   3. The sensor arrays 36, 40 1800 can include only temperature        sensors or only pressure sensors or unequal numbers of each        kind. Those variants will limit the type of measurements that        can be obtained but in certain applications those limited        measurements can suffice. For instance the sensor array 36 may        include only temperature sensors while the sensor array 40, 1800        may include temperature and pressure sensors. Other permutations        are possible without departing from the spirit of the invention    -   4. The pressure sensors can be differential pressure sensors        provided, for example with a channel to reach measuring        locations. The pressure sensors could also be associated to        Venturi or orifice calibrated flow channel to form a flowmeter,        as discussed previously.    -   5. Pressure sensors can be dynamic pressure sensors measuring        pressure waves propagation; they could serve as geophone        measuring acoustic waves propagation to determine geological        composition as in seismic surveys.

The SAGD installation also includes a series of observation wells 50that include sensor arrays 52. An observation well, in the example shownin a vertically drilled structure that extends into the steam chamber,or relatively close to it and that can accommodate a sensor array 52.Typically, an observation well 52 will not be used for steam injectionor for extraction of heavy oil. The depth of an observation well canvary depending on the intended application. In the example shown, theobservation wells 50 extend deeply within the steam chamber and theyreach the injector well 18. Variants are possible. The observation wells50 can be less or more deep or they can be formed at varying depths, forexample some observation wells 50 can be drilled deeper than otherobservation wells 50.

The sensor arrays 52 installed in each observation well 50 includetemperature sensors located at known intervals. As in the case of theinjector and producer wells 18 and 20, the position of the respectivetemperature sensors in the observation wells 50 is known with respect toa certain reference, such as the lower extremity of the well. In thisfashion, when a certain temperature sensor reports a temperature valueit is possible to determine with a relative degree of precision withposition within the well where the temperature measurement was made.

The sensor arrays 52 may include, in addition to temperature sensors,pressure sensors as well. Different combinations can be considered wheresome observation wells 50 include pressure and temperature sensing pairswhile other observation wells 50 include only temperature or onlypressure sensing pairs.

The sensor arrays 52 are made in the same manner as the sensor arrays36, 1800 and 40, namely using optical fibers with Bragg gratings toprovide the pressure and temperature sensing, among other possibilities.

The sensor arrays 52, 36, 1800 and 40 include a sensing segment thatincludes the Bragg gratings and a non-sensing portion without Bragggratings and whose function is to channel the optical signals forconveying the temperature and the pressure measurement data. In the caseof the injection and the production wells 18, 20 the non-sensingsegments extend along the vertical portions of the wells including theheels, where measurements are not made. Note however that this is amatter of design and the sensing segment can be made longer or shorterdepending on the application. One example of an application where thesensing segment extends beyond the horizontal portion of the productionwell 20 is the case where the production well 20 includes an in-linepump (not shown in the drawings) to assist with the extraction of theheavy oil. In such applications, it may be desirable to obtainmeasurements within the pump, such as the temperature of the heavy oilin the pump, the temperature of pump components, pressure values orboth. In such scenario, the sensing segment can be extended from theentire horizontal portion of the production well 20, through the heelthereof and up to a point where it reaches the pump. Alternatively, twoserial sensing segments can be provided where one is located at the areaof the pump while the other is located at the horizontal section of theproducer well 20.

As best shown in FIG. 4, the sensor arrays 36, 1800, 40 and 52 allconnect to a data acquisition and processing system. Typically the dataacquisition and processing system would be located above ground; howeverit is possible for fully automated installations to locate the systembelow ground. The data acquisition and processing system 400 includes adata acquisition module 402 and a data processing module 404. The dataacquisition module 402 connects to the sensor arrays 36, 1800, 40 and 52and derives from those sensor arrays temperature and pressure data. Morespecifically, the data acquisition module 402 includes the optical andelectronic components to inject an optical interrogation signal in thesensor arrays 36, 1800, 40 and 52 and to sense the responses to theoptical interrogation signals.

The responses of the Bragg gratings to the interrogation signal can bederived by sensing Bragg grating reflections or transmissions in theoptical fiber. The reflection approach is generally simpler since thesensing element, the one picking up the signal reflection is collocatedwith the optical source, the one generating the interrogation signal. Atransmission approach would also theoretically work but it requires foreach sensor array 36, 1800, 40 and 52 a second optical path, to conveyto the data acquisition module 402, the components of the interrogationsignal transmitted through the Bragg gratings. The second optical pathcan be a second optical fiber running in parallel to the one containingthe Bragg gratings. Both optical fibers are coupled to one another attheir extremities that are remote from the data acquisition module 402.

In a specific form of implementation, frequency multiplexing is used fordistinguishing the responses of the various Bragg gratings from oneanother. Each Bragg grating in the sensor arrays 36, 1800, 40 and 52 istuned to operate within a specific frequency window. By “frequencywindow” is meant a frequency range in which the response of the Bragggrating can vary depending on the strain applied to the optical fiber.By sending an optical interrogation signal that has a frequency rangespanning all the frequency windows, all the Bragg gratings are in effectinterrogated. The combined responses of the Bragg gratings are receivedsubstantially simultaneously by the data acquisition module 402 wherethey are de-multiplexed, such as by passing then through filters, toseparate them. Since each Bragg grating operates in a distinct frequencywindow, isolating that frequency range from the other frequencies allowsdetermining the degree of strain applied on the optical fiber at thelocation of the Bragg grating. The degree of strain is the deviation ofthe frequency response in the window with respect to a certain frequencyreference point.

The output of this process is therefore a series of strain valuesassociated to respective frequency windows. A map is provided in thedata acquisition module that correlates the frequency responses torespective locations of the Bragg gratings in the sensor arrays 36,1800, 40 and 52, such that it is possible at that point to determine theposition of the Bragg grating that has produced a given strain value.The position can be expressed in three dimensional coordinates or withrelation to a certain reference point, for example, 15 feet aft of theheel of the injector well 18, or in any other suitable manner.

Once the data acquisition module 402 has mapped the strain values torespective Bragg gratings, the strain values are then converted totemperature or pressure measurements. In most cases a linear relationexists between each read strain value and the corresponding temperature.In the case of pressure, the relationship is not so direct since thestrain acting on the optical fiber is the combined result of temperatureand pressure effects. However, since the strain resulting fromtemperature is generally known, especially in the case of collocatedsensing pairs, the strain induced in the optical fiber as a result ofpressure can be computed, thus deriving a pressure value.

The various optical and electrical components used in the dataacquisition module 402 used to perform the functions described above aregenerally known and it is not deemed appropriate to further describethese elements.

The output 406 of the data acquisition module 402 therefore generates astream of pressure and temperature values correlated to locationinformation associated with those measurements. This represents aprofile of temperature and/pressure values in the subterranean formationestablished along the sensor array. The level of granularity of thetemperature and/or pressure profile is dependent on the spacing betweenthe individual sensors in the sensor array. The format in which thosetemperature, pressure and location values are output can vary withoutdeparting from the spirit of the invention. In a simple example, theoutput format can be a table format mapping a location data, expressedas three-dimensional coordinates, temperature and/or pressure value andalso a time stamp, the time stamp indicating the time at which thetemperature and/or pressure where read.

A more detailed block diagram of the data processing module 404 is shownin FIG. 5. The data processing module has a computer based platform andincludes a Central Processing Unit (CPU) 500, a machine readable storage502 also referred to as “memory”, an Input and Output (I/O) module 504.The CPU 500, the memory 502 and the I/O 504 communicate with one anothervia a data bus 506. The memory is encoded with the program instructionsthat are executed by the CPU 500 to process the temperature and/orpressure values output by the data acquisition module 402. Thetemperature and/or pressure values are supplied to the data processingmodule 404 via the I/O 504. Results of the processing are output alsovia the I/O 504. The results of the processing may displayed on amonitor, printed on paper, or conveyed in any other suitable way to aninterested party. The processing that is performed on the temperatureand/or pressure data by the processing module 404 is an analysis of thesubterranean formation that uses principles of mass, energy or momentumconservation. The subterranean formation is a closed structure and byaccounting for mass/energy/momentum entering or leaving the closedstructure, it is possible to develop a model of the structure tocharacterize it from a structural point of view or from a dynamic pointof view. The temperature and/or pressure measurements provide datapoints at known locations in the closed structure that register events,such as mass/energy/momentum changes in the fluid in the closedstructure. Those changes can be used to derive useful information.

The process is described in greater detail in FIG. 37 which is aflowchart that represents the various steps of the program stored in themachine readable storage 502 and executed by the CPU 500. The processstarts at step 3700. At step 3702 pressure and temperature data arecollected from the sensor array 36, 1800, 40 and 52, as describedearlier. Note that while the sensor array 36, 1800, 40 and 52 is onlyused as an example; it is possible to use different data collectiontechnologies without detracting from the spirit of the invention.

At step 3704 a model of the subterranean formation is generated. Themodel is a collection of data that normally resides in the machinereadable storage 502. The data is a three dimensional representation (inany suitable format) of the subterranean formation, or a sub-structurethereof, subdivided in discrete areas. The collected temperatureand/pressure values are assigned to the various discrete areas.Accordingly, the three-dimensional model of the subterranean formationdepicts temperature and/or pressure variations in the underground fluidfrom one discrete area to another.

The subdivision of the subterranean formation into discrete areas isclosely tied to the actual sensor array 36, 1800, 40 and 52 and itsplacement in the subterranean formation. It is generally desired toassociate at least one sensor in the sensor array 36, 1800, 40 and 52with a discrete area, thus in most instances there will be at least asmany discrete areas as there are individual sensors in the sensor array36, 1800, 40 and 52. For applications that require a pressure data pointand a temperature data point for each discrete area, the number ofdiscrete areas will be associated with at least a pair of individualsensors.

The relative orientation of the discrete areas will depend at least tosome extent to the orientation of the sensor array 36, 1800, 40 and 52.With reference to FIG. 3, which shows an SAGD type installation wheresensor arrays are placed in the production and the injection wells 18,20 the subterranean formation is effectively divided into discrete areasthat join each other along respective planes which are generallyperpendicular to the direction of extent of the sensor arrays. In thisexample, the discrete areas are analogous to vertical slices takenthrough the subterranean formation, which in this case is the tar sandreservoir. The relationship between the actual sensors and theboundaries of the slices can vary. One possibility is to position theslices in the model such that the boundary between two adjacent slicescoincides with a sensor or to position the slices such that a sensor islocated in the center of the slice or in any other position that isremote from the edges of the slice.

For arrangements where the sensor array runs generally vertically, as isthe case with sensor arrays 50, the subdivision of the tar sandreservoir can be done in a similar way with the exception that theslices are made generally horizontally.

The reader skilled in the art will appreciate that there are otherpossible ways to divide the subterranean formation into discrete areas.For instance, the discrete areas do not need to be of uniform size orshape or all sliced in the same orientation. The subdivision process islikely to be specific to each individual extraction installation.

The modeling operation can also be applied to sub-structures of thesubterranean formation, not always to the entirety thereof. Examples ofsub-structures include conduits in which fluid flows. In the context ofan SAGD installation, the injection and the production wells 18, 20 areconduits can be modeled. Typically, a man-made conduit is easier tomodel since its geometric configuration is well known. A conduit has asize and boundaries that known in advance and this allows creating aprecise and accurate model.

At step 3706 the mass/energy/momentum changes between discrete areas aredetermined. This process uses the temperature and/or pressure readingsassociated with the respective discrete areas. If the temperature and/orpressure readings associated with different discrete areas change, thosechanges reflect physical events occurring in the fluid whose temperatureand/or pressure is being measured. By applying mass/energy/momentumconservation principles, it is possible to perform an analysis of thesubterranean reservoir or predict future events. This is shown at step3708. Specific examples of computations of properties of thesubterranean formation will be provided later.

At step 3710, the computed information about the property of interest ofthe subterranean formation is output via the I/O 504. In a specificexample, the output step may include displaying the information to auser via a display monitor, recording the information in a file or a logor transmitting the information for further processing or storage.

Alternatively, the computed information can be used to generate commandsignals to directly regulate the operations of the extractioninstallation.

A specific example of implementation of a data processing module,programmed to directly control an SAGD installation is shown in FIG. 6.The I/O 504 outputs control signals over data lines 604 that aredirected to steam injection component 600 used to regulate the injectionof steam into the injector well 18. Similarly, control signals are alsoplaced on data lines 604 and directed to the production well control toregulate the operation of the production well control.

In the case of the steam injection, the control signals can vary thesteam injection process. The regulation can include:

-   -   1. Start the steam injection process in the injection well 18;    -   2. Stop the steam injection process in the injection well 18.    -   3. Increase or decrease the rate at which steam is injected in        the injection well 18;    -   4. Regulate the temperature of the steam injected in the        injector well 18, such as increasing the temperature or        decreasing it.

In the case of scenarios 1, 2 and 3 the control data can be applied to asuitable valve in the steam line to perform the desired operation. Inthe case of scenario 4, where temperature regulation is desired, thecontrol signals are directed to the water heating device that generatesthe steam in order to perform the steam temperature regulation.

The regulation of the production well 20 via the control signals fromthe I/O 504 may involve the following:

-   -   1. starting the flow of heavy oil in the production well 20;    -   2. stopping the flow of heavy oil in the production well 20;    -   3. Increasing or decreasing the rate at which heavy oil flows in        the production well 20.

The implementation of scenarios 1, 2 and 3 depends on the way heavy oilis transported through the production well 20 to the ground surface. Ifthe oil flows solely by virtue of the pressure differential between thesteam chamber the ambient pressure at the surface, a control valve maybe provided in the production well 20, which can be operated by thecontrol data generated by the I/O 504 such as to regulate the flow ofheavy oil. The control valve may be located in any suitable location,typically near the ground surface. In instances where a pump is used totransfer the flow of oil, with or without steam pressure assist, thecontrol signals from the I/O 504 regulate the operation of the pump,such as shutting the pump down to stop the flow of oil, start the pumpto initiate the oil flow operation or increase or decrease the rate ofoil flow by varying the speed of the pump or the selective use of gaslift.

Also, the rate of energy supplied to the reservoir, as well as itslongitudinal distribution, can also be regulated in real-time accordingto the thermal and pressure measurements in-situ. For example, theinjector well could be provided with several steam injection pointsspaced apart along its length. The injection points are regulated byautomatic valves along it such that each injection point can be setindependently to deliver a desired amount of steam. The in-situmeasurements discussed earlier, namely the temperature and/or pressuremeasurements can be processed to derive a steam injection profile, alongthe length of the injector well such that the energy chamber radius orgrowth rate is longitudinally (with relation to the longitudinal axis ofthe injector well) generally uniform. Such uniform growth rate can beaccomplished irrespective of geological differences in the underground.For instance, the geological parameters of the subterranean reservoirmay vary along the length of injector well. The geological differencesmay be such that at certain locations the chamber may have a tendency togrow faster than other locations, when the steam delivery rate isconstant along the length of the injector well. In such instances, thechamber is unlikely to grow in a uniform manner. By modulating the steaminjection delivery profile according to the geological pattern, namelyby reducing the rate of steam injection in areas that normally growfaster and increasing the rate of steam injection in the areas thatnormally grow slower, it is possible to grow the chamber in a moreuniform manner.

In a similar fashion, longitudinal distributed heavy oil collectionports with individually controlled valves in the production wells couldbe used to create a determined heavy oil collection profile along thelength of the production well. In this fashion, the heavy oil rate ofcollection will vary longitudinally; more oil will be collected at onelongitudinal position of the production well than from another. In thisfashion, it will be possible to maintain a desired level of meltedbitumen pool all along the production well length regardless oflongitudinal geological and rate of heavy oil production variations.

Another possibility is controlling the rate of steam release to insureit does not liquefy before reaching the well end, thus creating anun-heated section in the reservoir. This can be detected by atemperature reading at lower value than the phase transition (steamtemperature).

Yet another possibility is controlling pumping rate of heavy oil toavoid flashing in the upstream section of the production well. As themixture of bitumen and pressurized liquid overheated water is pumped tothe surface, that mixture is subjected to a pressure drop along the flowpath. If the pressure becomes too low, the superheated water willvaporize (flash) and may damage the equipment. Flashing conditions willdepend on temperature, pressure and water content. The system canmonitor temperature, pressure and water content and thus determine ifthe risk of flashing exists anywhere along a segment of the flow path.If the risk is detected an alarm can be triggered. Alternatively, thesystem can automatically change operational parameters to reduce therisk of flashing.

Another possible application of the system is controlling the speed andtemperature of the extracted fluids to avoid overheating and damagingsome system components, such as the pump.

Yet another possible application is controlling the pressure in theunderground chamber by adjusting steam delivery to enable bitumenmobilization, while avoiding damage to structures close to theunderground chamber. The rock cap is an example of such structure whichcan be damaged and literally blown away if the steam pressure exceedsthe structural resistance of the rock cap. Another possible structurethat can be damaged in this way is the fresh water table. If the freshwater table is close to the reservoir wall and the steam pressure is toohigh, the steam can puncture the reservoir wall and penetrate the freshwater table.

More generally, the data processing operations performed by the dataprocessing module 404 can be used for different purposes in the contextof the exemplary SAGD installation. Examples include:

-   -   1. In-situ monitoring of the heavy oil extraction process    -   2. Determination of geological parameters of the SAGD        installation;    -   3. Reservoir field planning

In-Situ Monitoring of the Heavy Oil Extraction Process

The data collected by the data acquisition module 402 is processed toperform a monitoring of the SAGD installation which can be used toregulate operational parameters of the SAGD installation. Specificexamples of the monitoring that can be performed include:

-   -   Determining the yield profile along the horizontal section of        the production well 20.    -   FIG. 7 is a schematical view of the production well 20 shown in        cross section, also illustrating the position of two temperature        sensors 700, 702. The arrows illustrate the flow of heavy oil        through the production well 20. The volumetric flow rate Q_(B)        at the location B, which is the location of temperature sensor        700 is given by the following equation:

Q _(B) =Q _(A) ±Q _(IN)  (1)

-   -   Where Q_(A) is the volumetric flow rate at location A, which is        the location of temperature sensor 702 and Q_(IN) is the        volumetric flow rate of heavy oil passing through the segment of        permeable lining between the locations A and B. Q_(IN) can be        derived from sensing the propagation of thermal transients. The        thermal variation of the heavy oil passing through the        production well 20 is measured by sensor 702 at location A and        with a delay (Δt) by sensor 700 at location B, but with an        amplitude T_(B). Assuming that differences in the density and        heat capacity of the fluids are negligible, mass and energy        balances can be expressed as:

Q _(B) ΔT _(B) =Q _(A) ΔT _(A) +Q _(IN) ΔT _(IN)  (2)

-   -   where T is the temperature. Using T_(A) as the reference        temperature, a constant flow area (S) and negligible variations        of flow speed (V) in the production well 20 between the two        positions (A and B):

Q _(av) =V S=S(A−B)/Δt=Q _(A)±½Q _(IN)  (3)

-   -   This leads to a formulation to calculate the amount and        temperature of fluid flowing through the perforated liner in        that slice:

Q _(IN)=[2S(A−B)/Δt]−Q _(A)  (4)

T _(IN) =[Q _(A)(T _(B) −T _(A))/(2Q _(IN))]−T _(A)  (5)

-   -   Theses two equations can be solved for each slice (segment A-B)        by starting by starting at a location where the volumetric flow        rate is known. Once such location would be the heel where the        volumetric flow rate corresponds to the volumetric flow rate        produced at the surface since no additional heavy oil is        introduced in the production well 20 downstream that point.        Therefore, assuming that location B is the heel of the        production well 20, Q_(B) will equate the volumetric flow rate        delivered by the production well at the surface. The above        equations therefore allow deriving Q_(A) and Q_(IN). By working        backwards (in a direction toward the toe end of the production        well 20, Q_(IN) can be determined for every segment of the        production well 20 bound by temperature sensors. On the basis of        the computed Q_(IN) values and the associated location data in        the production well 20 (segment of the production well 20        associated with a Q_(IN) value) the yield profile of the        production well 20 can be determined. The yield profile would        show, for example, which segments of the well are the most        productive.    -   A similar but more refined approach can also be applied by        taking into account additional factors such as variations of        density of the heavy oil, heat capacity, fluid flow speed and        flow section. The resulting mathematical formulation would be        more complex but still solvable as long as an initial parameter        such as Q_(B) is available.    -   Determining the steam delivery profile along the horizontal        section of the injector well 18.    -   The approach described above could be followed to determine the        profile of steam delivery along the horizontal section of the        injector well 18. In this case, the amount of steam injected in        the well and flowing through the heel is known (this is the        amount injected at the surface). Equations 1 through 5 can be        used to determine the value Q_(IN), which in this example will        be negative since steam is exiting the injector well 18. Here, a        more refined approach that takes into account variations of        density of the steam as it flows through the injector well 18        would be beneficial since steam is inherently a compressible        fluid.    -   Determining the fluid level and composition over the length of        the production well 20.    -   The steam chamber in the SAGD reservoir is at saturated        conditions, so pressure and temperature of the chamber is        usually known, it can also be measured using instrumented        observation wells. In consequence, the pressure and temperature        over the bitumen pool is known, the temperature and pressure at        the bottom of the pool can be determine by the sensors reading        in the producer well, directly when liners effect are negligible        or by correcting for it. Considering that the bitumen pool is        essentially composed of molten bitumen and liquid water, we can        use their specific properties to determine their relative        proportion using the measured temperature gradient and liquid        column weight. For purpose of illustrating the principle that        can be applied to compute the height (H_(LP)) and composition (%        oil) of the liquid pool, one can assume a two phases liquid pool        (water and oil) with linear variation of specific weight (ρ) and        thermal conductivity (k) with composition:

ρ_(liquid)=%_(oil) ρ_(oil)+(100%−%_(oil))ρ_(water) =ΔP _(LP) /H_(LP)  (6)

k _(liquid)=%_(oil) k _(oil)+(100%−%_(oil))k _(water) =ΔT _(LP) /H_(LP)  (7)

-   -   Since the properties of the oil and water phases are known and        both ΔP_(LP) and ΔT_(LP) are measured in-situ, an easily        solvable system of two equations and two unknowns: %_(oil) and        H_(LP), is obtained. And so, for each spatial increment (sensor        in the series of sensors placed in the injector well 18 and        production well 20), the height and composition of the liquid        pool can be computed. If the relationships of specific density        and thermal conductivity with respect to composition are        non-linear, the equations would also be solvable as long as the        non-linearity can be defined.    -   Determining the fluid incoming in the pool over the production        well 20.    -   The calculations are made periodically to obtain average dynamic        values over the calculation period, typically 1 minute. A mass        balance over the pool for that calculation period can be used to        determine the amount and composition of fluid that penetrate        into it during that time. Equations 1 through 5 can be used to        determine the value Q_(IN), which correspond to the amount of        fluid existing the pool, in this example we will assume that the        fluid has a constant composition, the same as in the pool in the        beginning of the calculation increment. By applying Equations 6        and 7 at the beginning and at the end of the calculation        increment, we can determine the variation on the amounts of        bitumen and water in the pool during the increment. Since, we        know for each component the increase and the amount that has        left the pool, we can calculate the amount that entered by a        simple subtraction. More precise measurements can be obtained        either by reducing the calculation time increment or by using        average or integrated values during the increment in combination        with iterative algorithms.    -   Determining the heat delivered along the injector well 18.    -   Equations 1 through 5 can be used to determine the value Q_(IN),        the amount of steam exiting the injector well 18 between two        sensors and since we are using pressure-temperature sensors, we        can calculate its latent enthalpy, or the energy generate during        its condensation, from standard thermodynamic tables. We can        then easily determine the profile of energy delivered to the        reservoir by multiplying the flow rate by the calculation        increment period and the average latent energy.    -   Determining the characteristics of the newly energized layer of        the chamber.    -   Since the steam chamber is at saturated conditions, we can        assume that there is no lost of mass or energy through it. So,        all the steam existing the injector will rise to the chamber        edge without mass or energy losses and then will serve to heat        up the reservoir ground, heat-up its bitumen contain and        mobilized it, so it flows downward by gravity into the bitumen        pool, the free space liberated by the bitumen being replaced by        steam. Energy balance on this newly energized layer over the        calculation incremental time will equalized the amount of energy        incoming to the sum of the energy consumed to heat-up the layer        and mobilized the bitumen plus the energy lost on the edge of        the chamber. The energy incoming is equal to the energy existing        the injector, due to the saturated nature of the steam chamber,        and the energy lost outside the chamber can either be calculated        using a semi-infinite solid or a more complex model or be        monitored by an observation well having distributed thermal        sensors. Global mass balance on the calculation slice can be        used to calculate the amount of bitumen liberated and the amount        of water used to replace it, or the apparent porosity of the        newly energized layer. The amount of water retained in the newly        energized layer is simply given by the amount of steam exiting        the injector well over that particular calculation slice and        calculation time minus the amount of water entering the pool        over the same period and slice. A similar balance can be done on        the bitumen, leading directly that the amount of bitumen        mobilized is equal to the amount of bitumen entering the pool.        The apparent amount of energy used to mobilize the bitumen is        simply the energy consumed in the newly energized layer during        the calculation step divided by the amount of bitumen liberated.        So, we obtain two geological parameters: the apparent porosity        and the apparent bitumen mobilization energy; knowing the        different geological phases composing the newly energized layer,        we can calculate the dimension of this layer. Observation wells        can be used to monitor the energy chamber growth and confirm the        calculation; in that case, these measurements can be used to        determine the layer dimension and the apparent geological        properties can be used to determine more precisely the        geological phases it contains and would globally give the same        apparent resulting properties.    -   Alarm system to signal that potentially steam may be breaking        through the production well 20.    -   Such an alarm system monitors the temperature along the        horizontal segment of the production well 20 through which heavy        oil is being collected. The temperature monitoring at the        production well provides a series of temperature values, each        associated with a certain location with respect to time. The        temperature of the steam injected in the injector well 18 is        also monitored. Both temperatures are compared and if they get        too close to one another, which is an indicator that the steam        head over the heavy oil pool approaches the production well 20,        the flow rate of heavy oil through the production well 20 is        reduced to avoid steam break through. This is best shown in FIG.        8 which is a schematical illustration of the SAGD installation        showing the relationship between the steam head, the heavy oil        pool, the injector well 18 and the production well 20.    -   As FIG. 8 shows, in practice the horizontal sections of the        production and the injection wells 20, 18 are rarely perfectly        straight. In most cases they are of wavy nature. Accordingly,        the distance that separates the injector and the production        wells 18, 20 vary along the length of the wells. During the        operation of the SAGD installation, steam is injected from the        injector well 18 and forms a steam head 800 that sits atop a        heavy oil pool 802. The pressure of the steam, acting on the        heavy oil drives or at least assists with the passage of the        heavy oil through the permeable lining of the production well        20. Normally, the level 804 of the oil pool remains well above        the production well 18. This is the case when the rate at which        heavy oil is transferred out of the pool 802 is less than or        about the same as the rate at which oil flows into the pool as a        result of steam mobilizing oil in the subterranean reservoir.    -   In instances where the rate of oil extraction has been set too        aggressively and exceeds the rate at which the pool is        replenished or for some reason the rate at which the pool is        replenished drops suddenly, the level 804 will drop and expose a        portion of the production well 20 to the pressurized steam. This        will cause a steam break-through where pressurized stream can        flow through the production well 20. Since the steam is at a        very high temperature (in excess of 200 degrees C.), the steam        flow can damage the oil production well 20 and related equipment        above ground that is not designed to withstand such high        temperature fluid.    -   A correlation exists between the temperature in the production        well 20 and the level 804 of the heavy oil pool 802. In        particular, when the temperature in the production well 20        approaches the temperature of the steam chamber 800, this is an        indication that boundary between the steam chamber 800 and the        heavy oil pool 802 is close to the production well 20.    -   The temperature that can be considered “critical” in the sense        of indicating an imminent steam break-through will vary        according to the intended application. In a first possibility,        that temperature is a preset value. When the temperature of the        steam chamber is well known and assumed to be generally uniform,        the critical temperature (T_(C)) is set at that value,        optionally taking into account a safety factor. For example,        when the temperature in the steam chamber is approximately 250        degrees C., with a safety factor of 20 degrees C., T_(C) is set        a 230 degrees C. Evidently, the safety factor can vary according        to the intended application and can also be omitted if desired.    -   In use, the temperature in the production well 20 is        continuously compared to T_(C). If the temperature exceeds        T_(C), which indicates that a steam breakthrough may occur, an        alarm is generated to alert a human operator, and/or a        corrective action is initiated. The temperature comparison        process is a multi-step operation. Each temperature value from        the sensor array 40 is compared to T_(C). Since the horizontal        portion of the production well 20 is not straight, hence its        spacing from the steam chamber 800 boundary varies, the        temperature reported by the temperature sensors 42 a . . . n, is        unlikely to be the same. For instance, in FIG. 8, the zone A        shows a portion of the production well 20 that is closer to the        boundary of the steam chamber 800 than the adjoining portions of        the production well 20. The temperature in the production well        20 is likely to be more elevated in that area than in an        adjoining area of the production well 20. Longitudinal        variations in the rate of bitumen mobilized in the reservoir and        flowing down to the bitumen pool, as well as variations in the        restrictions in those specific flowing paths, also contribute        significantly in the level variations along the bitumen pool.        One possible monitoring strategy is to trigger an alarm when any        one of the temperature values reported by the sensor array 40        equals or exceeds T_(C). Another monitoring approach is to        trigger an alarm only when a set of adjacent temperature sensors        report a temperature equal to or exceeding T_(C). This variant        offers the advantage of protecting against false alarms due to a        faulty sensor or a localized rise in temperature that is due to        a steam-breakthrough.    -   Another criteria to detect potential steam breakthrough is the        rate of change, either local temperature increasing or local        pressure decreasing in the producer. Although the absolute value        will indicate catastrophic event, the rate indicates how fast it        is about to append and how much time we have to re-act or        re-adjust.    -   The monitoring process that would be performed by the data        processing module 404 is illustrated by the flowchart at FIG. 9.        At step 900 the temperature of reported by a temperature sensor        42 a . . . n is compared to T_(C). If T_(C) is exceeded, as        determined at comparison step 902, an alarm is triggered at step        904. Otherwise, the loop continues with the comparison step 900        performed between the temperature value reported by the next        temperature sensor 42 a . . . n and T_(C).    -   In addition to or instead of triggering an alarm, a corrective        action can be implemented automatically. The corrective action        can include reducing the rate at which heavy oil is being        transferred through the production well 20, for in turn reducing        the rate at which the pool of heavy oil 802 is being depleted.        The reduction can be operated by controlling a valve in the oil        path to reduce the rate at which oil flows and/or regulating the        operation of a pump (reducing the pumping speed) if a pump is        used to transfer the oil.    -   Another possible corrective action is to reduce the rate of        steam injection so as to lower the pressure in the steam        chamber. This can be accomplished by regulating a valve in the        steam flow path leading to the injection well 18.    -   Another possibility that can be considered for monitoring the        SAGD for steam-breakthrough conditions is to compare the        temperature in the production well 20 to the temperature        measured in the injection well 18. This allows a more precise        temperature assessment in the steam chamber, more particularly        in the area close to the boundary between the steam head 800 and        the heavy oil pool 802. This approach is useful in instances        where the temperature in the steam chamber may not be considered        constant along the length of the injection and production wells        18, 20 horizontal sections. This approach is illustrated by the        flowchart in FIG. 10.    -   At step 1000 the temperature between a temperature sensor 38 a .        . . n in the injector well 18 (say the one nearest the heel) is        compared to the temperature reported by a temperature sensor 42        a . . . n in the production well 20 that is in proximity to the        sensor in the injector well 18. This will be the temperature        sensor 42 a . . . n, closest to the heel of the production well        20. The comparison can be made by taking into account a safety        factor of the desired magnitude. A specific example could be 20        degrees C. Accordingly, if at step 1000 the temperature in the        production well 200 plus the safety factor equals or exceeds the        temperature in the injector well (step 1004) then the alarm is        triggered, as shown by step 1002. If the comparing step 1004 is        answered in the negative (no alarm) then the processing        continues at step 1006 where the temperature sensor index in the        injection well 18 and in the production well 20 is incremented.        In this fashion the next run through the processing loop will        compare the temperature between the next two vertically aligned        temperature sensors. The process is run continuously to provide        an uninterrupted monitoring. The temperature values are thus        compared between vertically aligned sensor pairs, repeatedly        scanning the horizontal sections of the injector and the        production wells 18, 20.    -   As discussed in connection with the previous variant, the one        using the critical temperature T_(C), in addition to or instead        of triggering an alarm, corrective measures can be implemented,        including reduction of the rate at which heavy oil is        transferred out of the pool 802 or the rate and/or temperature        at which steam in injected in the steam chamber.    -   Yet another possible variant can be considered for monitoring        steam break-through conditions, which senses the weight of heavy        oil head above the production well 20. When the weight goes        below a certain value, which means that the level 804 is        dropping below a certain minimum and the production well 20 may        be uncovered, the alarm is triggered and/or corrective measures        are taken.    -   The pressure in the pool of heavy oil 802, at the level of the        production well 20 or slightly above it, is the sum of the        pressure resulting from the weight of the oil head and the sum        of pressure of the steam head. Assuming that the permeable liner        creates a negligible pressure drop, the pressure measured inside        the production well 20, via the pressure sensors 42 a . . . n,        reflects the pressure acting on the outside surface of the        production well 20.    -   The pressure in the steam chamber can be obtained by directly        measuring the pressure above the level 804 of the heavy oil pool        802. This can be done by using a pressure sensor in any one of        the observation wells 52. The pressure sensor can be identical        to the pressure sensors used with the sensor array 40, namely        based on a Bragg grating in series in an optical path with other        Bragg gratings used to report temperature measurements. The        heavy oil pressure, at any particular location is the pressure        reported by a pressure sensor 42 a . . . n at or near that        location minus the pressure in the steam chamber.    -   The process is illustrated best by the flowchart at FIG. 11. At        step 1100 the pressure in the steam chamber is read. As        indicated previously, the pressure can be measured by a pressure        sensor in anyone of the observation wells 50. At the next step        1102 the pressure is read from a pressure sensor 42 a . . . n in        the production well. The pressure would typically be read from        the first pressure sensor relative to a reference point, say the        heel. The pressure readings are compared at 1104. If the        pressure is below a certain minimal value, indicating that the        weight of the liquid head above the production well 20 is too        low for a continued operation without undue stream-breakthrough        risk, then an alarm is triggered, at step 1106. In addition to        the alarm or alternatively to triggering the alarm corrective        actions can be initiated, such as discussed earlier.    -   If the pressure difference assessed at step 1104 is within        acceptable limits, the processing continues at step 1108 where        the pressure sensor index is incremented. This in effect sets        the next iteration of the pressure monitoring to be run in        connection with the following pressure sensor in the sensor        array 40. The process is therefore repeated with every pressure        sensor 42 a . . . n, therefore scanning the entire length of the        horizontal run of the production well 20 for localized pressure        drops signaling the possibility of steam-breakthrough        conditions.    -   For more accuracy, it is possible to take into account the        pressure drop introduced by the permeable liner. This can be        accomplished by applying a mathematic model that simulates the        influence that the liner structure has on the pressure        measurement read within the production well 20. The application        of the model would modify the pressure reading such that the        resulting pressure value will more accurately reflect the        pressure acting on the outer surface of the production well. The        mathematical model used may vary according to the application.        One possible example is to use a model that is dependent in the        volumetric flow of heavy oil through the permeable liner; the        larger the volumetric flow the higher the pressure drop across        the permeable liner. The value Q_(IN) in the equations presented        earlier represents the volumetric flow rate of heavy oil through        the permeable liner. The model could therefore be:

P _(out) =P _(in) *A*Q _(IN)

-   -   Where P_(out) is the computed pressure acting on the surface of        the production well 20, P_(in) is the pressure measured in the        production well 20, A is a constant and Q_(IN) is the volumetric        flow rate of the heavy oil through the permeable liner.    -   In another possible variant the monitoring for        steam-breakthrough can be made by determining the height of the        heavy oil column above the production well 20 instead of looking        at the pressure value.    -   The difference (ΔT_(LP)) between temperatures measured in the        injector and producer wells 18, 20 can be used to compute a        thermal gradient in the heavy oil pool. For purpose of        illustrating the principle that can be applied to compute the        height (H_(LP)) and composition (% oil) of the liquid pool, one        can assume a two phases liquid pool (water and oil) with linear        variation of specific weight (ρ) and thermal conductivity (k)        with composition:

ρ_(liquid)=%_(oil) ρ_(oil)+(100%−%_(oil))ρ_(water) =ΔP _(LP) /H_(LP)  (6)

k _(liquid)=%_(oil) k _(oil)+(100%−%_(oil))k _(water) =ΔT _(LP) /H_(LP)  (7)

-   -   Since the properties of the oil and water phases are known and        both ΔP_(LP) and ΔT_(LP) are measured in-situ, an easily        solvable system of two equations and two unknowns: %_(oil) and        H_(LP), is obtained. And so, for each spatial increment (sensor        in the series of sensors placed in the injector well 18 and        production well 20), the height and composition of the liquid        pool can be computed. If the relationships of specific density        and thermal conductivity with respect to composition are        non-linear, the equations would also be solvable as long as the        non-linearity can be defined.    -   The computation of the height of the heavy oil head for        monitoring for steam break-through conditions may be more        precise in applications where the pool of liquid at the bottom        of the subterranean reservoir includes both oil and water. In        such case the pressure measurement used in the previously        described embodiment provides less reliable results since the        weight of the liquid head may not allow readily determining how        much oil remains above the production well 20. The weight of the        liquid head may be only oil, only water or a combination of        both. In those instances the determination of the height of the        oil head may a more precise measurement.    -   Feed-back controlled SAGD process example.    -   Now that we have an approach to monitor in real time well's        profiles of not only pressure and temperature, but also energy        chamber growth and bitumen pool level, the wells can be equipped        of distribution system of steam injection and bitumen extraction        using automated valves. Fluids extraction profile can be        controlled to maintain an optimal level of the bitumen pool all        along the well regardless geological variations, the automated        valves just have to be reacting to the calculated local pool        level. In the same way, the steam injection can be controlled to        maintain an optimal chamber growth rate all along the well        regardless geological variations, the automated valves just have        to be reacting to the calculated local chamber growth rate.        Designs for automated distribution system of steam and        extraction fluids exist, but in the absence of local measurands,        are not used since we have no criteria to adjust them.    -   Expert system for SAGD process example.    -   The proposed approach enables a wide range of new information        that serves for daily operation and also to better understand        the reservoir characteristics and behavior. In consequence, it        can serve as a base for an expert system continuously updating        reservoir characteristic, on which simulation can be run and        strategies tested for wells layout and operative scenarios. By        integrating it with daily operation, this expert system can also        manage the alarms and feed-back control automated operations.        Integrating the two aspects, it is possible to develop or refine        the geological model to take into account daily performances and        also develop a platform that can display the process full life        cycle (past and future as expected) to enable global        optimization; it can also generate an alarm if the response        differs from the expectation, enabling models and strategies        update to account for it, the expert system becoming self        monitoring and melting geological modeling, exploitation        strategies and daily operations into a single platform forcing        inter-considerations and enabling global optimization. For the        geological modeling, real-time in-situ apparent porosities and        bitumen mobilization energies can be combined to all other        geological characterization measurements, these constitute a        bank of global properties. A library of the individual        geological properties of all geological phases potentially        present can also be build. Then standard combination        optimization algorithms can be used to determine the most        representative geological phases repartition in the geological        model matching the ensemble of the measured properties bank.

FIG. 16 shows schematically an example of such a higher level systemwhich is an example of implementation of the invention. Therepresentation in FIG. 16 illustrates modules that perform functionswhich typically would be performed by software on the basis of thetemperature and/or pressure information supplied by one or more sensorarrays in the subterranean formation. The system 1600 includes thefollowing modules:

-   -   1. An in-situ monitoring system 1602, which includes the sensor        array as described earlier and the attendant data collection        devices. More specifically, the in-situ monitoring system 1602        includes in this example (1) collocated pressure and temperature        sensors along the injector, (2) spatially coordinated collocated        pressure and temperature sensors along the producer, (3)        collocated pressure and temperature sensors along vertical        observation wells in the steam chamber, where all the sensor        arrays are connected to the same surface units synchronizing the        data acquisition. Optionally, the in-situ monitoring system 1602        can be provided with sub-systems such as pump monitoring        temperature sensor, chemical concentration sensors, localized        flow-meters, etc.    -   2. A reservoir field planning module 1604 which uses the        temperature and/or pressure information to make        suggestions/recommendations about subterranean reservoir        planning;    -   3. A data integration and visualization module 1606 with a SAGD        simulator;    -   4. A geological model 1608 which describes the subterranean        formation;    -   5. An operational parameters module 1610 with includes an alarm        status management function to monitor well performance        deviations from models.

The system illustrated in FIG. 16 can be used to perform the following:

-   -   1. Initial/periodic geological measurements, such as seismic        surveys, core samples, LIDAR . . .    -   2. Real-time continuous well data logging, including temperature        and pressure profiles in the injector, producer and observation        wells; fluid pool level profile monitoring; computation of        incremental apparent porosity and bitumen enthalpy of        mobilization for newly steamed region during time step; alarms        status level, such as local pool level, ESP overheating, etc. .        . .    -   3. Real-time continuous operational data logging, including        steam injected temperature, pressure, flow-rate and toe/heel        ratio, as well as, producer flow-rate;    -   4. Real-time visualization and alarm reports, including those        generated by operational parameters module 1610 and also        deviations from actual chamber growth and performance from the        ones predicted by models;    -   5. Generation of geological phases data bank; well layout        scenarios, including retrofits; operational scenarios, such as        steaming and extraction strategies;    -   6. Multiple dimension, such as 4D visualization with or without        history revision to include latest information; geological        model, including steam chamber and fluid pool growths;        performance parameters resulting from scenarios, including        instantaneous and cumulative extraction rates and steam-to-oil        ratios and bitumen mobilization ratios.    -   7. Real-time geological model corrections based on in-well        measurements and including steam chamber and fluid pool growth;    -   8. Studies of operational scenarios, via the SAGD simulator,        based on actual well conditions;    -   9. Planning of wells layout, including retrofits, in association        to operational scenarios before and during exploitation;    -   10. Upgradeability to include other field measurements, even in        real-time; to change in well configurations, including        multi-ports adjustable injector and/or producer; to process and        manage auxiliary information such as ESP aging, field        containment, etc.

The system 10 can assist the operator of the extraction installationwith the following:

-   -   1. lowering the sub-cool while preventing steam breakthrough        through distributed monitoring in the producer;    -   2. well layout planning to reduce the occurrence of poor        performing wells;    -   3. retrofitting wells planning to increase in service wells,        either by adding injector and/or producer;    -   4. adjust operational parameters to steam chamber growth in        real-time to avoid cold zone inclusions;    -   5. optimization tool for instantaneous and cumulative ODOR, SOR        & mobilization fraction.

The examples of implementation of the invention discussed earlier usingmass/energy/momentum balances on in-situ multi-point measurements oftemperature and/or pressure applied to the SAGD extraction process canalso be used in the context of other extraction installations. Forinstance, a similar approach can be used to model a VAPEX extractionprocess by modifying steam/water properties to include the physicalproperties of the solvent solution injected in the well. Cyclic SteamStimulation (CSS) would also require a simple adaptation as this processis similar to SAGD but it uses a single well, working alternatively asan injector and then as a producer. Steam chamber growth can bemonitored by applying the model for the injector during the steamingperiod; and bitumen and steam chamber depletion can be modeled using theproducer analysis during the extraction phase; successive steamingphases would then take into account the mass and energy of steam tocomputationally re-build the old steam chamber, prior to monitoradditional steam chamber growth with the SAGD approach.

Toe to heel air injection (THAI) processes do not use steam to energizethe reservoir, but controlled internal combustion inside the wellcontrolled by metering the amount of oxygen supplied. The multi-pointtemperature and pressure monitoring enables identifying the location ofthe combustion wave and the amount of energy it generates throughcombustion gases temperature and pressure. The same approach of applyingmass and/or energy and/or momentum balances on successive slicescharacterized by thermal and pressure measurements can be tailored forspecific THAI process variants. The same approach can also be used forextraction processes using buried electrodes to generate the energy tomobilize the oil. In this instance, the main advantage to monitortemperature and/or pressure along the electrode is to be able tocorrelate the actual energy input with predicted profiles in theextraction model. Deviations from the predicted profile allow detectingareas of the electrodes that are less effective in supplying energy,which phenomena occurs as a result of a non-uniform aging of theelectrodes along their length.

Energy can also be required a subterranean formation to mobilize thegeological resource not due to its high viscosity, but due to lowporosity and permeability. These resources can be oil, even light oil,as in shale oil; gases, as in shale gas, sand gas or tight gas; or evenheat as in geothermal wells. Two major approaches are used to extractthese types of resources: water flooding, with or without solvents, andhydraulic fracturing. The invention can be used to monitor waterflooding processes in a similar way as it used to monitor a liquid poolheight and composition in the bitumen pool of the SAGD process. Pressuremeasurements can be used to determine the liquid column height and thetemperature measurements can be used to determine the thermalconductivity of the liquid, and so, its composition. Also, since thetemperature of the liquid used for flooding is different than thesubterranean formation, a temperature wave or gradient can be monitoredby the multi-point thermal measurements and used to calculate flows andcontributions similar to equations (4) and (5). Specific mass and/orenergy and/or momentum balances formulation, as well as multi-pointtemperature and/or pressure monitoring arrays will need to be adapted tospecific flooding and well layouts.

Hydraulic fracturing consists in flooding a subterranean formation withpressurized fluid, usually water, containing small particles. The fluidpressure is increased until it is able to fracture the rock surroundingthe well in which the pressurized fluid is being injected. Thepressurized fluid enters the cracks in the rock and causes the cracks togrow. The crack growth continues until the fluid pressure drops belowthe rock strength. When no more fluid is injected into the well, thecrack propagation stops, the fluid pressure stabilizes and fluidmovement stops. The small particles carried in the fluid settle into thenewly formed cracks to prevent those cracks from closing when the fluidpressure drops.

Hydraulic fracturing is usually done by pressurizing successive sectionalong the well depth, each section separated from the other by temporaryplugs, such as swellable packers. This process increases considerablythe permeability of the reservoir section surrounding the well. Thisprocess is more and more used to extract oil and gas trapped in rock andsand formations, as well as to increase heat extraction in large scalegeothermal energy station.

Since this process creates multiple channels having very smallcross-sections, flow inside them generates both a significant pressuredrop and thermally traceable signatures by either viscous dissipationfor fluids or Joule-Thomson effects for gases. So, the combined abilityof measuring multi-point temperature and pressure inside the well inwhich the pressurized fluid is injected can be used to derive flows inthe cracks in addition to the flow in the well. For illustration, butwithout limiting the invention, a specific example will now be providedof how the invention can be applied in the context of a natural gasextraction installation using hydraulic fracturing.

FIG. 38 illustrates in cross-section a tight gas well 3800 where naturalgas is trapped inside shale rock. The first portion of the well 3802,which is near the surface just serves to reach the deeper sectionscontaining gas reserves. The following sections 3804, 3806 and 3808 arethe producing zones and are separated by swellable packers 3810. Asensor array 3812 is placed in the well and extends through the zones3802, 3804, 3806 and 3808. The sensor array 3812 includes multipletemperature and pressure sensor pairs to provide to an operator at thesurface with temperature and pressure measurements at various depths inthe well. The sensor pairs are identified by 3814. The sensor array 3812is inserted through a through a pressure seal at the well head 3816.

In a specific example of implementation, the sensor array and thepressure sensor illustrated in FIG. 35 can be used for this application.

Measurement locations coincide with the locations of the pressure andtemperature sensing pairs 3814, which are concentrated in the producingzones 3804, 3806 and 3803, although some sensors could also be placed inthe leading zone 3802. For simplicity, this example considers that eachmeasurement point monitors both temperature and pressure, but adifferent arrangement is possible where only pressure or temperature ismeasured, or the number of thermal sensors is different from the numberof pressure sensors.

The hydraulic fracturing process is performed consecutively for eachindividual section 3804, 3806 and 3810. Each section 3804, 3806 and 3810is isolated from each other by injecting fluid into the packers 3810 ateach end of the selected section, the fluid causing the packers to swelland form seals. Then fracturing fluid is injected into the sealedsection 3804, 3806 and 3810 until the trapped fluid pressure raises highenough to crack the rock. Once the desired level of fracturing has beenreached, the fracturing liquid is removed and the swellable packers aredeflated. The same process is then performed on other sections until allthe producing sections 3804, 3806 and 3810 are cracked.

The hydraulic fracturing liquid contains small particles that get wedgedin the newly formed cracks and prevent them to close back as thepressure is released. Pressure higher than the rock resistance isrequired to crack the rock, and so the sensor array 3812 should be ableto sustain this high pressure while reporting accurately the pressureand without collapsing or damaging the temperature and/or pressuresensors. Preferably the sensor array 3812 is capable of sustainingoutside pressure without collapsing and reporting accurately thepressure of at least 30 MPa, preferably of at least 50 MPa, even morepreferably of at least 70 MPa and yet more preferably of at least 80MPa. The pressure reporting function at those pressure levels impliesthat the deformable component is designed to allow for sufficient rangeof motion, the mechanical link is designed such that it transmits strainto the optical fiber within the range that the optical fiber cantolerate (the optical fiber will not be damaged) and structurally theassembly will be strong enough to sustain the pressure.

It is preferred to design the sensor array such that it is in factcapable to structurally resist to even higher pressure levels in theevent a pressure spike arises. At a certain point, the pressure is sohigh that the deformable component is at the end of its range of motion(completely compressed or completely expanded) and can no longer reportaccurately the pressure. However, structurally, the assembly can stillsustain the outside pressure. For example, it is possible to encounterpressure spikes up to 120 MPa in a well and the sensor array is designedto withstand those pressure levels without collapsing or undergo anyother permanent damage. In this example, as the pressure rises above thelimit at which the pressure function works, the sensor array will stopreporting accurate pressure values but once the pressure falls belowthat level then the accurate pressure reporting resumes.

The sensor array 3812 is inserted through the swellable packers 3810,usually passing into a slit in each packer 3810 that can swell to form acomplete seal around the sensor array 3812. Small diameter sensor arrayscan provide the desired crush resistance and at the same time theability to be inserted into a swellable packer while allowing theswellable packer to achieve an effective seal. It has been found that asensor array 3812 having transverse dimension of less than 0.60 inchesworks well. Preferably, the transverse dimension is less than 0.5inches, more preferably less than 0.35 inches and most preferably isless than 0.25 inches. The transverse dimension is the maximaltransverse dimension if the cross-section is not circular. An ovalcross-section is an example of a non-circular cross-section. Note thatit is not absolutely necessary to provide the sensor array 3812 with aconstant cross-sectional dimension along its entire length. Thecross-section can vary. To achieve the desired seal it is advantageousto provide the sections of the sensory array 3812 that pass through theswellable packers 3810 with a cross-sectional dimension which falls inthe ranges above, but the sections of the sensor array 3812 that arelocated between the swellable packers 3810 can be made larger.

The multi-point pressure and temperature measurements can be used toderive a series of information at the different step of the hydraulicfracturing process.

At a pre-fracturing stage, the in-situ monitoring can be used toestablish the native subterranean formation characteristics in term oftemperature and pressure that can be used later on as a base line toevaluate flows through temperature and pressure data in the well 3800.The well drilling process can affect these native parameters by creatinga pathway between the underground and the surface, and by potentiallyforming a skin layer around the drilled conduit. In consequence,monitoring for a reasonable time the down-hole conditions in the sealedwell may be useful to enable recovering the stable conditions by lettingthe reservoir environment diffuse through the well skin. The in situmulti-points temperature and pressure sensors enable the monitoring ofthe stabilization of these conditions, even locally, to determine whenthe native reservoir conditions are reached. This way also, the drillingeffects can also be evaluated. The formed skin thickness andpermeability can be calculated by deriving the Joule-Thomson effectcreated by the gas flow through the skin.

For analysis purposes, the well can be modeled in consecutive horizontalslices having a pressure and temperature measurements at its center.These slices are considered uniform so the read pressure and temperatureare applied on the whole volume of the slice. In this fashion, it ispossible to calculate the mass of gas that each slice contains at everychronological increment. This application of the mass conservationtheory implies that the mass flow rate in the skin during thatchronological step is equal to the variation of mass in this slicedivided by the duration of the chronological step. The mass flow ratecan be supplied to the momentum balance in the skin as well as thepressure and temperature on both sides of the skin; on the well side,the average pressure and temperature during the chronological step; andon the reservoir side, the temperature and pressure obtained afterreaching equilibrium. The momentum balance can then be combined with theenergy balance in the skin which is characterized by the frictiondissipation and Joule-Thomson effects as parameters; one could alsoinclude a parameter for the skin thermal specific heat. For thecalculate flow rate, only one set of flow conduit length and crosssection will solve simultaneously the momentum and energy balance. Thismethod enables obtaining the skin permeability and thickness profile.

Once the skin layer profile is modeled, it can be matched to thedrilling operational data to deduce the drilling effects and potentiallycontrol them for adjacent future wells. If adjacent wells exist,correlating the new well's instrumentation response to operationalchanges observed in the adjacent wells can be used to determine interwell communication effects. These effects can be quantified using areservoir model and even allow adjusting to more realistic values thepermeability and porosity used in the model.

During the hydraulic fracturing operation, the presence of in situthermal and pressure monitoring sensors can be used for a number ofpurposes. As discussed earlier, hydraulic fracturing is usually donesuccessively on specific zones by confining the pressurized fluids intoa specific zone, by using swellable packers. Monitoring for temperatureand/or pressure changes in the adjacent zones serves to validate thatthere is no leakage, or to quantify the level of leakage, through theswellable packers. Since the temperature of the pressurized fluids isdifferent than the one the reservoir, fluid migration is indicated bysensing a moving the thermal front, which indicates that leakage ispresent. Since the flow rate of the fluid injected in the well and thewell dimension are known, the mass balance can be expressed withequations similar to equations (4) and (5), thus quantifying leakage.Pressure measurements on both sides of the swellable packers, associatedwith the calculated flow rate, can be used in a momentum balancecomputation to determine the leaking channel cross-section. Similarly,both type of measurements, associated with similar balances, can be usedinside the zone being hydro-fractured to monitor the cracking fluidprogress and coverage of the zone.

As the amount of fluid injected in the zone increases, its pressure alsoincreases until it reaches the surrounding rock ultimate cracking value.When this value is reached, cracks start to form in the rock and thepressure suddenly drops a bit as the fluid penetrates in the newlyformed cracks. Since the mechanical properties of the rock usually varyslightly along the well and pressure stabilizes rapidly inside the zone,the weakest rock fraction will tend to crack first, weakening it evenmore. In consequence, the natural tendency is to create long, large andnumerous cracks in the weakest rock and little to none in the strongestrock. This creates very permeable pockets in an almost unchangedpermeability reservoir, resulting in a poor extraction.

Real-time dynamic computation on the basis of pressure and temperatureprofiles in the pressurized zone (updated at the appropriate timeinterval), enables to determining where the cracks are created and wherethe fluid went, and to adjust fluid injection and pressurizationaccordingly to reach ultimate rock pressure at the strongest side beforethe cracks created in the weakest portion reach too far. This real-timefeedback loop permits obtaining much more uniformly cracked zone in termof permeability, so as to mobilize a higher fraction of the gas trappedin the reservoir. One important step is to insure that cracking fluid ispressurized uniformly throughout the zone before the weakest crack isformed, so a slow injection rate is preferred during this phase. Oncethe rock starts cracking, an immediate fast pressurization permits toreach fracture stresses for the strongest rock portion prior a too farpropagation in the weakest rock, and so to initiate cracks all along thezone. The uniformity of crack propagation is then controlled byadjusting fluid injection on the basis of the monitored thermal andpressure profiles.

Since the fracturing fluid contains small particles, such as fine sand,to prevent the created crack to close down, these small particles cancreate plugs that clog up flow in the supplying line, the well or thenewly formed cracks. Here again, in situ monitoring of temperature andpressure can be used to determine flow profiles, and so, detectclogging. Once a clog is detected, fluid injection pulsation can be usedto create pressure wave to break down the plugs, since these fluids arealmost incompressible, sudden increases of fluid injection rate have ahammer effect. Since, the in situ monitoring permits determining theflow of fluid entering in the cracks along the zone, it is possible tocalculate the profile of the volume of cracks created using local massbalances. The dynamic analysis of the pressure and temperaturevariations in each modeling slice enables determining the length of thecracks. If there are instrumented adjacent wells, their potentialthermal and pressure responses can also be used to determine if partialcommunication has been created between the wells, and so, determinenewly created cracks length and concentration. Finally, the amount ofenergy supplied to the well can be calculated.

When the hydraulic fracturing is performed, pressure is released byletting the cracking fluid expand in the newly formed cracks. Onceagain, the in situ thermal and pressure monitoring enables computinginformation by using mass, energy and momentum balances. In a firstrapid step, fluid will exit to release extra pressure (excess pressureover the pressure in the native well); during that phase, there will bealmost no fluid motion in the cracks. Once the fluid pressure dropsunder the reservoir pressure, the gas will start to push the liquid outof the cracks and exit to the surface. This motion can be monitoredsince, the gas and liquid are usually at very different temperatures. Inaddition, since the cracks form long and narrow channels, viscous energydissipation occurs as a result of the liquid flow, causing a thermalincrease at the well side of the cracks. The level of thermal increaseis a function of the crack length and its cross-section. As the liquidexits the crack, the effective length decreases, and so does the viscousdissipation. Once all the fluid has been expulsed from the crack, onlythe gas flow remains, which can be modeled as gas flow in a pipe betweenthe reservoir pressure and the well monitored pressure. Mass, energy andmomentum balances can be applied on this pipe flow considering aconstant reservoir pressure, viscous dissipation, Joule-Thomson andintegrated volumetric well flow rate to compute the crack length andcross-section. These calculations can be performed on a slice by slicesection containing individual monitoring points or on a fractured globalreservoir model with three dimensional porosity and permeability.

After the release of the fracturing fluid, the well will simply releasethe gas under reservoir pressure to the surface through the cracks andthe well. The restricted flow in the cracks will drive the process, theflow in the well being quasi uniform except for the gravity component.Once again, the flow in the cracks can be modeled as flow in a pipebetween reservoir pressure and well monitored pressure, but this timethe reservoir pressure can not be considered constant, rather it can beconsidered as a fixed volume reservoir. Mass balance on this fixedvolume considering the flow rate in the cracks as a negative componentwill determine its pressure drop chronological profile (pressure dropover time). Similar mass, energy and momentum balances as discussedbefore can be applied on this pipe flow model considering a constantreservoir pressure, viscous dissipation, Joule-Thomson, integratedvolumetric well flow rate, previously established crack length andcross-section. By combining these to the mass balance of the fixedreservoir volume, dimension of the pocket of mobilized gas, as well asgas quantity it contains, the gas that can flow out through the crackcan be obtained. This can be used to establish the global production ofthe fractured well and to update the reservoir model. From the updatedreservoir model the layout of future adjacent well can be planed.

During the lifetime of the well, the in situ monitoring can serveadditional purposes. As mentioned before, the in situ instrumentationresponse during adjacent wells fracturing can be used to determine thelengths of the newly created cracks in this adjacent well and the levelof communication they create between the two. This information can beused to control the fracturing process of the adjacent well to mobilizethe desired section of the global reservoir. Continuous monitoring ofthe depletion of fractured section surrounding the well and thecalculated liberated gas pockets can be used to detect cracks cloggingor collapsing that could re-trap the desired reserves and calculatetheir amount. Dynamic behavior of those events can be used to segregatebetween clogging by heavier hydrocarbons and cracks collapsing. Knowingthe amount of re-trap reserve and the trapping mechanism are importantinformations to decide on the relevance of either cleaning the well withsolvent solution to un-clog the cracks or to perform another hydraulicfracturing to reopen collapsed cracks. Having thermal and/or pressureprofiles enables locating where these remedial operations are requiredinstead of risking of increasing the permeability all along the well andcreating undesired inter-well communications or extending its reach overthe desired section of the global reserve.

Integrating all these in situ and balances into a field level reservoirmodel enables the operator to optimize his well layout and hydraulicfracturing operations to minimized capital and energy to extract themaximal gas percentage out of the reserve. It can also be used to insurethat the hydraulic fracturing will not liberate hydrocarbons resourceinto surrounding environment, especially water tables; nor weaken theground structure and liberate the trapped hydrocarbons by soil settling.

The examples provided earlier should not limit the scope of theinvention as many variants are possible. The invention allows performingmulti-point measurements along the well to generate profiles instead ofaverage values. Combined with the mass and/or energy and/or momentumbalances, profiles of geological behaviors can be generated whichenables the detection of energy thief zones and energy storage zones, aswell as quantifying sectional contribution to the production andresource three dimensional mapping. Using a high frequency multi-pointmonitoring system enables detecting dynamic events propagation andcalculates flows of material and energy using the balance equations.This innovative approach can be applied on almost any type of geologicalformation, but is especially useful for processes using energy tomobilize the desired resources since it permits to quantify bothdelivered energy and liberated resources profiles along the well.

Although various embodiments have been illustrated, this was for thepurpose of describing, but not limiting, the invention. Variousmodifications will become apparent to those skilled in the art and arewithin the scope of this invention, which is defined more particularlyby the attached claims.

1. A sensor cable for measuring pressure at a plurality of spaced apartlocations in a subterranean formation, the sensor cable comprising: (a)a first sensing portion including an elongated outer casing having afirst end portion, a second opposite end portion and a side portionextending between the first end portion and the second end portion, thefirst sensing portion including a pressure sensor to measure pressureacting on the side portion; (b) a second sensing portion including anelongated outer casing having a first end portion, a second opposite endportion and a side portion extending between the first and second endportions of the second sensing portion, the second sensing portionincluding a pressure sensor to measure pressure acting on the sideportion of the second sensing portion; (c) an interconnection portionlocated between the first sensing portion and the second sensingportion, the interconnection portion including a first end portion and asecond opposite end portion; (d) the first end portion of the firstsensing portion being coupled to the first end portion of theinterconnection portion; (e) the first end portion of the second sensingportion being coupled to the second end portion of the interconnectionportion; (f) said first sensing portion, said second sensing portion andsaid interconnection portion when coupled to one another forming anelongated string-like structure; (g) an optical fiber defining acontinuous optical path extending through said first sensing portion,said interconnection portion and said second sensing portion, saidoptical path configured for transporting an optical signal conveyingpressure information generated by the pressure sensor of said firstsensing portion and the pressure sensor of said second sensing portion;(h) said first sensing portion, said second sensing portion and saidinterconnection portion having a cross-sectional dimension that remainssubstantially constant along the string-like structure; (i) the firstsensing portion, the second sensing portion and the interconnectionportion include respective first, second and third internal cavities,the sensor cable including a fluid-tight partition between the firstinternal cavity and the third internal cavity.